How to balance combat encounter for magic user group that suddenly can't cast magic? [closed]

Question

My campaign is set on a low-magic setting, meaning magic is not common. Magic users are generally welcome, although at some places they hate magic users.

Most (80%) of my players start off as a magic user, sorcerer, warlock, wizard, ranger, bard, arcane trickster, eldritch knight, etc. despite this premise. I allowed (so many of) them, but reminded them there might (or will) be consequence later for magic users.

Now I'm at the point of revealing that magic taints the world, and thus must be very carefully used, unless they want to permanently worsen the corruption. Because of this, I expect the players to opt not using magic at all, including magic items. The party is at level 4 now, and I expect them to reach 5-6 when this happens.

How to balance combat encounters to be level appropriate, if, in worst case, they won't/can't use magic at all?

The party relied on two warlocks to deal AoE damage on previous encounters. If I'm to use several lower CR (CR 1 or 1/2) monsters, I'm worried that they might be overrun by the monsters. On the other hand, if I use one or two monster with more CR appropriate, I fear they are too powerful because of their abilities. I can tone down the HP or attack/damage/abilities, but I'm trying to preserve their original statblock as much as possible, even including resistance/immunity to non-magical piercing/bludgeoning/slashing damage.

More information:
I'm expecting 5-6 people per session from a pool of 10. Only two of them goes pure non-magical path.

Although the question is how to balance combat encounters, I'm also open to solution that does not directly modify how encounter works, such as suggesting to multiclass ahead of time (I'm currently planning this as a last resort, though).

Note: Corruption is a term I use to explain mutation of nature. When first understood, it is framed as a bad thing. It does not, however, kill the land, but it alters nature to something "unworldly". The simple thing is appearance of giant spider and worm is a mutation from the normal spider and worm.

Answer 1

You are screwed

Sorry to be the bringer of bad news, but you've painted yourself into a corner here. You told your players that magic users are "generally welcome, but some places hate them". This to me sounds similar to how you'd expect to be treated when you play a half-orc or a monster race. Some places will hate you, but overall you should be fine.

Now at level 5, you suddenly intend to tell them that "yeah, magic was a terrible thing all along and if you use it, you're going to ruin the world". You've essentially just screwed over your magic users, because either they now become bad guys who don't care that they're destroying the world, or they make a new character that isn't magic.

A wizard that can't use magic is just a commoner with a fancy hat. There's no point in them multiclassing at this point because they'll permanently have 5 levels in worthless classes and they won't be able to keep up with any of the pure classes.

If you absolutely insist on going through with the idea, you should most likely just count all levels in a magic class as being not-there for the calculation.

So if you have a wizard 5, warlock 2 / fighter 3 and a barbarian 5, calculate the experience for an average encounter with only the non-magic levels, so: A level 0, a level 3 and a level 5. Classes like paladin and Eldritch Knight might need some fine-tuning for this concept, but considering you've essentially thrown the CR system out of the window anyway, you might be able to figure something out for them.

In addition, you will need to avoid all monsters with resistances to piercing/bludgeoning/slashing, because their CR will now be way off because you lack magical damage. Don't even go near monsters with immunity to those.

Answer 2

The best way is to not do this

You've started a campaign with a vague warning to your players that magic-users may face consequences. Your players probably expected witch-hunts or something similar, not a nearly complete removal of their characters' powers under the threat of tainting themselves. Intentionally or not, you've been misleading your players into building bad characters. It can cause frustration to the point where I wouldn't be surprised if people walked out of your table (I would).

The balance aspects are similarly grim. By practically disarming your magical characters --- 8 out of the 10, total --- you've basically rendered the idea of having balanced combat encounters (using the usual notions of balance) hopeless. Two of the characters have powers they can use. Eight don't. No matter of tweaking your combat encounters will change that.

Note that I'm not saying that your magical characters will be constantly useless or helpless. You can certainly devise encounters where they have things to do that don't involve spellcasting. However, being delegated to performing menial support tasks or dealing scratch damage with backup melee attacks is not balance. The caster characters are still only strong when casting, which you've deprived of them. Even if you allow them to multiclass, they'll be hopelessly behind the Muggle PCs if they start multiclassing this late.

Therefore, I urge you to drop this idea. If you want balanced encounters or balanced gameplay in general, start by not breaking the balance in the first place.

Answer 3

You were supposed to deal with this in Session Zero

Session Zero is before the campaign starts, you make your players well aware of playstyle, campaign narrative and style, how rail-roaded things are, and make sure their characters fit together, have a backstory that works for the party, and make sure that they didn't screw themselves.

As others have pointed out, you're going to be putting characters who are "level 5" down to about "level 2" in power-level. If you start throwing CR 5 monsters at them, despite their extra HP it will probably be a "Deadly" encounter anyway.

Unless your players really understood that you were going to nuke their characters you should probably not do this.

So what do I do

I'd look to either have them rebuild their characters through some kind of quest. They find out that their magicks are destroying the world and that they need to become battle-hardened warriors instead. They travel to some place and worship a strange deity, go through a training montage, and poof! They've been cleansed of their magical corruption and are ready to fairly approach the rest of the campaign.

Balancing encounters

They're seriously around CR2 or CR3 even at level 5 if you take away their biggest character attributes. The best bet is to start off low and adjust CR's after you see what they're capable of.

That said, I am pretty sure your players will hate this. If PCs are allowed to die and the player can re-roll, I would expect the players to immediately suicide their characters honestly; in order to have one with appropriate skills.

Answer 4

Rather than restricting your players, let them adapt

As many of the other answers suggest, it is a bad idea to try and balance encounters around the idea that spell casters won't use their spells at all as the challenge ratings in 5th edition can't really account for this. I would instead let players adapt and change their characters after this revelation. Something that lets them continue on at the same power level, but maybe with some substantial changes. Here are a few potential solutions that aim to do that.

Firstly I would separate out arcane and divine spell casting. I encourage you to only make arcane spell casting a problem, an allow any divine casters (eg. clerics, rangers, druids etc.) I would also allow magic items. They can be rare in a low-magic setting, but I would rule they don't taint the world any further, magic involved in their creation has already been released.

Secondly I would consider allowing arcana cantrips, ruling that they are minor magics that don't defile or irreparably damage the world, even if they are frowned upon by the populace. This would maintain the combat viability of most caster classes and they can stick to their bread and butter damage spells (eg. Firebolt, Eldritch Blast, etc.)

So with that said here are the options I would give your players:

Swap to a non-arcane class/subclass

For a subclass this is fairly easy, let an Eldritch Knight or Arcane trickster renounce their magic abilities and return to another mundane subclass. Because of the morally good deed involved in this sacrifice I would also maybe let them keep a cantrip, effectively granting them the 'magic initiate' feat for free.

For a full arcane class (wizard, sorcerer, etc.) I would similarly give them a chance to completely sever there connection to magic, if they switch to a divine spell-casting class of the same level. This could be represented by a Lawful/Good deity that sees there noble deed and rewards them with divine Cleric abilities. Or become a Paladin with a special oath to never cast arcana magics again. Sorcerers might be able to become a divine soul in order to remain there class but others could become Clerics with a divine entity replacing their primary casting stat with Wisdom.

As a bonus this could be role-played very well with wizards destroying their spells books as an offering to the gods.

Remain an arcane caster

It is possible that your character might decide remain an arcane spell-caster anyway.

There are two ways you could introduce mechanics that support your campaign without limiting these players.

First is related to the legality/acceptability of magic in civilisation:

In order to distract witnesses from the casting or to make them think a magic item was used, as a Bonus Action a character may attempt a Charisma (Deception) or Dexterity (Sleight of Hand) skill check (player’s choice) with DC equal to 8 + the level of the spell being cast. If the character fails his or her check and the DM rules that there is a witness, the character will be receiving a visit from the authorities. For bards this might be easier or done with the Performance skill since their casting is woven into music or oratory.

For example, William is a 5th-level wizard who attempts to cast a magic missile at a thug that has jumped him. He wants the spell to have a little extra punch, so he casts it using a 3rd-level spell slot. Not wanting anyone to rat him out to the authorities, he tries to do it without anyone realising he used magic. The DC for his check is 11 (8 + 3).

The second is to deal with the damage their magic does to the world:

I would borrow from the Dark Sun setting here, where all arcane casters are either 'Preservers' or 'Defilers'. When casting a spell a character can either attempt to be careful and preserve the natural life force surrounding them or choose to defile. To preserve you could let characters use a higher spell slot or pass a check similar to above perhaps and Arcana check base DC of 8 + the spells level. Evil or Chaotic characters may not have an issue with this at all since they can defile but this not only permanently damages their surroundings but may upset others and have consequences.

When this is pitched to the players it should be about giving them choices rather than taking it away. It could lead to a very memorable campaign if done right, and since you have so many casters, each one could take a very different path, and the effects that has could be interesting to see.

Answer 5

Serve them with some fava beans and a nice chianti

My campaign is set on a low-magic setting, meaning magic is not common. Magic users are generally welcome, although at some places they hate magic users.

So far, so good. Low magic campaigns can work very well.

Most (80%) of my players start off as a magic user, sorcerer, warlock, wizard, ranger, bard, arcane trickster, eldritch knight, etc. despite this premise.

They didn't believe you. You have an expectations mismatch, and they are In-Character unaware that magic is on a declining trend. Just how much in-world lore and information did you provide to the PCs to foreshadow the corruption of magic?

• If none, then you set them up to fail.

• If a lot, then perhaps your players didn't want to believe that you'd hamstring their chosen character/classes.

I allowed (so many of) them, but reminded them there might (or will) be consequence later for magic users. {snip}
Because of this{the corruption}, I expect the players to opt to not using magic at all, including magic items. The party is at level 4 now, and I expect them to reach 5-6 when this happens.

You expect this, but what concrete information did you offer that they are able to plan with?
What cues about magic going awry have already been in evidence in play?
The lack of detail about your custom world makes this hard to answer, and harder to play as a player when you spring this on them. The concept itself, the corruption, isn't by itself something unplayable. It's the blind side hit that is the problem.

What to do now?

How to balance combat encounters to be level appropriate, if, in worst case, they won't/can't use magic at all?

1. Have them multiclass

2. Let them roll up new characters.

3. Reconsider how severely you want to penalize magic use.

   You have written yourself into a trap based on an expectations mismatch. In the core rule books of D&D 5e, to include the introduction of the PHB, it is stated very clearly that magic suffuses the multiverse, the Weave is a thing, and any player who reads the PHB has an expectation, if they choose a magic using class, of being able to play the character that they chose.

Course of Action 1: He who lives by the magic, dies by the magic.

Your players didn't believe you when you said it was low magic, and that there would be consequences. Let them discover that you weren't bluffing. Then, have them roll up new characters ... if they still want to play at your table.

You set them up for failure: what were you expecting the result to be?

Course of Action 2: Clean out the Taint

1. A quest to clean up magic, or some kinds of magic, is presented.
   Have a quest for them to complete that gets at the source/root of the taint in magic. Since you seem to have borrowed from Robert Jordan's Wheel of Time taint theme, follow through.
2. Make a distinction between "light" and "dark" magic and make the consequences for each different. This is a very old storytelling trope, the difference between dark and light magic. Make an adjustment such that your casting classes can call on a limited resource in their efforts to clean the taint out of magic in your world. Some spells work, but some don't, or have harmful side effects. (Heh, evil grin here's a chance to make liberal use of the Wild Magic Sorcerer table ... )
3. Make the quest "in serial" so that certain quest goals clean up, say, some cantrips, or a few divine spells. Another quest cleans out a school of magic at levels 1 and 2. And so on.

Third Course of Action: Psionics FTW

Go to WoTC web site and get the third "psionic" Unearthed Arcana. Allow some of them to respec as Mystics. It's not magic, it's psionics. Problem solved.

Answer 6

Unlike most everyone else here, I don't see a problem here at all. You warned people that magic use has consequences:

Most (80%) of my players start off as a magic user, sorcerer, warlock, wizard, ranger, bard, arcane trickster, eldritch knight, etc. despite this premise. I allowed (so many of) them, but reminded them there might (or will) be consequence later for magic users.

They chose to ignore it. Maybe this is what they want to happen. Frankly, if my DM warned me during character creation that, "At some point, there will be consequences for magic use," I would not at all be surprised if, suddenly, there were dire consequences for magic use! You told the PCs that magic wasn't going to be reliable like it is in most campaigns. I'm struggling to think of what else the party might think you meant.

Let the story play out as presented, particularly if the PCs are going to be responsible for resolving the problem with magic in the world. I would change little to nothing, although I might drastically step up the foreshadowing.

About the biggest change I might consider would be to allow cantrips to be used with minimal or no difficulties from full spellcasters (and only full casters). In that instance, a spellcaster still has not insignificant combat abilities.

Furthermore, all your PCs can multiclass. Especially if you time it right, you can set it up so that the PCs will be 80% of the way through level 4. When they hit level 5, they'll know they need to pick up some armor and weapon proficiencies. I find it unlikely that none of them could multiclass to fighter or rogue; very few players will dump Dex as a spellcaster.

I'd also recommend allowing your PCs to select feats. Feats are a good non-magical way to increase combat power. You may also wish to use the Alternate Rewards section from the DMG to grant non-magic item rewards to your players.

Finally, if it's really not working, you can always change to a different campaign. "The PCs fail because the players made poor decisions," is a perfectly valid way for a campaign to end.

---

As to the actual question for encounter balance:

In spite of what many people think, encounter balance is extremely flexible in D&D 5e. IMX, combats go bad due to bad die rolls more than anything. In order for the Short Rest mechanic to work, the game's designers set the standard encounter difficulty low so that each adventuring day could accommodate the 6-8 encounters that are required to have multiple Short Rests. If your full spellcasters have access to cantrips (i.e., they still have something to do in combat roughly on par with a weapon attack), I do not believe that you'll need to change anything at all until you get to very high level (level 13 or higher). At worst, all you've done is make the Standard difficulty into Hard or Deadly. That's not bad; it just means that your PCs will have to be more discriminating about combat and more reliant on hit dice and long rests for healing.

The only other thing I see happening is that, at higher level, many obstacles require magic to overcome. Planar travel, magical diseases or curses, magical flight, flesh to stone, raise dead, freedom of movement, greater restoration, etc. All those become unavailable, so you'll have to be careful about the types of attacks your players suffer. You'll just have to be conservative at first, as well as generally flexible and willing to play it by ear.

At the end of the day, however, the published challenge ratings aren't going to be much help. Your PCs will still be just about as good against a Golem or Giants or Balor, for example, but against a Wraith or Medusa, the party is suddenly in much more trouble. You'll kind of have to play it by ear. It's difficult to give you a better idea because you haven't disclosed the nature or mechanics of the penalty for magic use.

As far as magic items, well, there should be absolutely no problem with that. As people so commonly repeat: the Monster Manual was not designed with the assumption that magic items would be available! That's partially why a Balor seems so wildly over CR (I've seen one die in a single round against a level 13 party, and two die in two rounds against the same party one level later). That means that, all things being equal, an average party should be expected to beat any appropriate challenge even if they're a bunch of melee characters fighting a Golem or Elemental!

At the end of the day, then, you can still use the game's built in Challenge system to build your encounters. The AC and HP values of monsters won't be a problem in and of themselves. What will be an issue is the monsters that have weird attacks or weird defenses, because the party will have few options against them, especially as their levels rise.

Answer 7

It ruins balance completely

However, having the idea of magic being spoiled for them completely may work. For a few sessions at least! If magic can taint or spoil so too should something magic be able to unspoil or untaint.

In the same place they learn about Magic being Bad News, have them find a clue to something that makes magic not corrupt within its influence. It makes them feel hopeless about using magic but, continues to provide a balance with not being able to use it and having to stick close to the party to use it safely. When players split the party in town, those split off won't be able to use magic safely. However, for combat encounters everyone will be close enough to the artifact to be able to use magic freely.

I did something similar in a previous campaign. The initial dread/despair they had as they realised my warning about magic being dangerous wasn't an idle DM threat was fantastic. It took my group about 3 sessions to debate about magic use, continue exploring, find the clue to "clean" magic, and grab the artifact.

I would probably drop a few lower CR "scavenger"-type enemies at them. A goblin or two may show that they don't have the firepower they used to and that enemies that previously were a cake walk will now be a challenge again. This will also give you a chance to see exactly how bad the balance has been thrown off so that you can choose enemies accordingly.

Not all combat ends with enemy death. If they can put up enough of a fight, enemies might flee because their opponent was tougher than expected.

Answer 8

Systematically you have problems as have been stated in many of the other great answers provided here...

You do have possible IN STORY answers to your problem depending on where you are going with the "tainted magic" angle. Your stated goal is to balance encounters but you have a "campaign wide" issue whereby your casters will have something taken from them but their enemies have not. You can balance that by either handing something back to the casters or removing benefits from the "monsters" they are encountering:

1. Take a little...give a little While you are removing casting provide a new answer in discovered technology. Discovering of the uses of gunpowder, steam cannons, alchemical enhancements etc. There are many concepts you can introduce that would act as general replacements for caster's powers and you can provide a natural conduit for your casters to move toward those playable options without losing the reasons most individuals choose casters.

2. Escalate the escalation Make the taint an escalating concept that would increase the caster's powers (updated damage, AOE, duration) while increasing the effects of the taint. This at least introduces a choice for your casters and may ease the angle where they feel they have been straight up robbed of the benefits from their chosen class. Introducing this while also providing them some in game outs for casting would also be preferable. Note: This would also create some balance issues as well if you ratchet up the power/taint aspect too quickly. A caster willing to sacrifice themselves to defeat the big bad may have serious ramifications for your campaign if unplanned for.

3. Take the fun away from EVERYONE The overall impact of removing (or adding a taint) to magic in a world will have massive impacts, not only on your delvers, but on all creatures. Monsters that primarily relied on magic as a means of defense or who themselves might have been inherently magical may find themselves unable to enter combat in the same fashion. Ideally you could throw some of these encounters at your party giving them a chance to fight on an evened playing field until they have sorted out how they will best approach their new combat options.

At the end there should be a give and take. Allowing the casters to choose from new options preserves their encounters (and the stats of your monsters long term) without forcing the players into a series of ever bad/boring choices for their characters. Once the plight they find themselves in is plain an out of game conversation would be required to ensure the players understand that this is a story/stylistic twist and not simply a way to screw them out of the fun they had anticipated when choosing casters in the first place. Replaced expectations are far better handled interpersonally rather than simply providing them no choices and therefore giving them a sense of ruined expectations.

Answer 9

Since most of the top-voted answers are some variation of "this can't work", I'd like to add some ideas to prevent you from dropping this great opportunity to make the game quite interesting.

Don't make magic vanish suddenly!

The worst thing to do would be to screw your magic users over by taking aways all their power at once and basically stripping them naked in front of the enemy. If you plan to remove magic unconditionally, at least give them a chance to adapt.

Anyway, I would refrain from just cutting away what is an essential part of most classes in the game.

Give the world spell slots

No, you didn't misread. Especially during encounters, it might make things quite intresting to prepare a sheet of spell slots for an environment. For example, the road on which the party gets ambushed might only be able to sustain 4 2nd level spells, while the area around the Magic Springs of Faeries might allow casting up to 5 3rd level spells and or an equivalent number of lower-level spells. All PCs and creatures in an area draw from the same pool of environment spell slots. As soon as those are used up, their spells start losing effectiveness. They lose damage dice, range, duration, whatever is appropriate for certain spells.

Let them play with the taint

You mentioned that magic taints and corrupts your world. Instead of robbing them or their magic, make this interesting to play with.

You could make it some kind of equivalent exchange. Let's say your wizard keeps throwing fireballs. This robs the world around him of warmth and at some point he might start shivering and even suffer cold damage. Vice versa, playing with cold magic and causes his surroundings to heat up. You would have to get creative with some spells, but I'm sure you could find interesting drawbacks for most of them.

Or, the other way round, you could let the magic develop it's own "mind" and get out of control. Sure, your fireball sometimes makes more damage, but sometimes it just explodes in your face before you can send it at an enemy.

For divine spellcasters, you could let them feel that whenever their gods use their power to help them, their antagonists become stronger. Sure, your player can send a prayer to heal the parties' wounds now, but maybe in the long run that causes a God of Death to amass more power and suddenly there is an army of undead walking around.

Let them feel the consequences

Let your players feel the consequences of corrupting the world. Maybe the common people despise them for their carelessness or even fear them. Maybe the end up destroying the environment and cause horrible creatures to spawn. Whatever they are, your players should have the agency to decide whether their characters suffer them or even find ways to use them to their advantage.

Basically, you can use combinations of these suggestions. Maybe your environment can sustain a certain number of spell slots and after spending those, horrible things start to happen. Maybe as equivalent exchange, maybe as certain spells becoming too strong to control, maybe just randomly transforming objects and creatures. But all of these should be more interesting than dropping your idea of a magic-corrupted setting or just taking magic away altogether.

Answer 10

Add a quest to allow players to swap out their casting class levels to non-caster ones.

This is assuming you won't change your worldbuilding. Make it clear that their spellcasting is harmful, but allow an exit in the form of character rebuilding. Make some quest to a fantastic destination where they can rebuild themselves and shear off these caster levels.

3.5e had something like this to allow players to change even their character's race, classes and other options (feats, skills).

Think like this: In the past other spellcasters have arrived at the same conclusion: to continue using magic would destroy the world. What did they do? Did they seek divine help? Did they find an artificer to make a magic item that can swap class levels?

It is your world, and your PC party is not the first one to go through this problem. There should be an answer in the world that can solve it. And the answer is adventure.

Answer 11

I don't know what mechanics you were planning on to nerf the magic, but are there ways you could create consequences for spells that don't force you to rebalance encounters so severely?

Depending on what is causing this tainting of magic, it could be a great place to pull out the madness traits, with saving throws getting more and more difficult for higher level spells. I suggest this only because it won't mess with mechanics too much, and when I ran OotA, my group adored the madness traits. They loved having these quirks to their roleplay and having the impacts of their travels be explicitly laid out, to the point where they were genuinely sad when they succeeded on madness saving throws, because they were having so much fun going crazy.

I find the most important question for me to ask as a DM is: Is this fun?

It's possible, as someone else suggested, that your party members are excited by the potential extra challenge caused by playing casters, and that that is why they chose to play them. I would probably have done the same, because that's a plot point that would appeal to me as a player. However, it's also possible they just didn't believe you, and will be upset if they lose combat abilities.

There have been a lot of really good suggestions-- my favorite being the idea of having the switch occur partway through level 4, so that they have time to realize that they're in trouble before hitting level 5 and multiclassing-- but I wanted to drop in the idea of madness, as well, because it sounds like this is a campaign and setting that might be well-suited to such a thing.

Answer 12

Examine your premise in light of global environmental scale

I'd like to point out some items that you might consider. If your world is so tenuously balanced that five or six people blasting away with magic could have any meaningful impact globally, then your world is doomed anyway.

Somewhere, some sorcerer's going to get goosed by a squirrel and launch a Wild Magic cascade and the whole thing goes to hell no matter what your PCs do.

So maybe you could shift scale. A few people using magic stops being not an issue. Maybe the problem is that entire nations and empires are based on Magic. That way, what was originally an engineering problem (Magic is tainting the world! Fix it!) becomes a social/environmental problem 'Magic-heavy societies are accelerating global magic toxicity! Get the word out and convince enough of the populace that magic overuse is bad, find sustainable magical methodologies, and save the planet'

Sure, there's no bad guy to fight in this case, just the usual magic change deniers, but frankly I'd struggle to play along with a premise like 'Magic corrupts the world, so individuals have to be super careful or one random miscast could doom us all'

Answer 13

Hope you have a fix planned already

I agree with most of the answers that you've kinda screwed yourself, but I wanted to toss in some input regarding ways I've seen magic-use restricted, and whether that was fun or not:

• A game I'm currently playing in, all magic users have to be careful about using their spells within the Feywild. Any spells cast there trigger Wild Magic surges from the sorcerer's chart, which can often have unintended consequences (party wizard is a good 8 inches shorter than when we started). Over the course of the game, we completed a quest chain that gave our party's Druid the ability to cast spells without reprisal in the Feywild as she had attuned to that natural space, but the restriction is still in place for the others. Our table found this to be pretty fun.
• Another game I played in, I was a spontaneous caster and we'd arrived at some sort of dead-magic area. Whenever I tried to cast a good 2/3s of my spell list I had to roll and often my spells either fizzled or didn't do what I wanted. Also, I lost the slot when this happened. I ended up moving before we finished that storyline, but I can tell you for the 6 sessions of it that we had, I wasn't really enjoying myself. It sucked because everything I tried to do was a total crapshoot through no fault of my own.

Balancing your encounters: Make everyone suck together, then adjust the CRs from there

First of all, it really sucks to be the magic-user at the table and suddenly be nerfed into obsolescence. At a minimum, I would consider a means to broadly nerf the group. So you nerfed all magic, but expand that nerf to include the fighter's magical weapons and armor. If there are none, maybe some sort of curse that saps the fighters' strength. It sucks to suck, it sucks more to suck alone.

In addition, I strongly recommend that if you're going to restrict magic the way you propose, you include a means within that statement on how to unrestrict it as well because otherwise, I'm not sure why I'm going to stay at that table otherwise. I also recommend that you exempt cantrips from that restriction from the get-go; players need to be able to do things in combat and shooting a crossbow I'm not terribly good with isn't fun. Perhaps also exempt rituals so that prepared casters have non-combat utility they can provide. I'd also recommend exempting healing magic unless you want things to regularly grind to a halt so healing can be done via hit dice.

By virtue of your proposal, you pretty much need to redraft the CRs of every monster and compare it to your player groups. Sucks for you. What sucks even more is that even if you do this, you will have to do it every time you permit the players regular access to more magic without restriction.

You've sorta written yourself into a corner, and unfortunately the best way out is fairly labor intensive as the DM.