Is this homebrew "Thoughtseize" spell balanced?

Question

[Note: This homebrew spell has been updated in a Part 2 post]

I was inspired by the Thoughtseize card from Magic, the Gathering to create a spell that achieves a similar effect.

Thoughtseize is a 1st-level Enchantment spell with a range of 30 feet. It requires Verbal, Somatic, and Material components (a needle or pin). Its description follows:

You probe the mind of your target, and can sever a thread of their memory for a time.

Choose a creature within range. The creature must succeed on a Wisdom saving throw, the DC for which is your spell save DC. On a failed save, the affected creature forgets one spell from their spell list of a level lower than the spell slot used to cast this spell (cantrips count as level 0). You may choose which spell is forgotten.

When this spell is cast at higher levels, you may select an additional spell for the target to forget for each second level after 1st.

If the targeted creature is currently under the effect of this spell, its previously-forgotten spells are restored to its memory (unless chosen again).

This effect lasts until dispelled or until the affected creature completes a long rest, whichever occurs first.

I am firstly looking for feedback regarding the language of the spell. I want to ensure the phrasing is as consistent with 5th edition's paradigm as possible. I am also concerned with balance. This is clearly not a damage-dealing spell in any way, but it certainly can be powerful, especially when cast early in combat.

Answer 1

Formatting

I think below may be a better way to phrase things to sync with 5e's standards:

Thoughtseize

Casting Time: 1 action [I assume]

Range: 30 feet

Components: V, S, M (a needle or pin)

Duration: Until the end of the target's next long rest¹

You probe the mind of your target, and can sever a thread of their memory for a time.

Choose a creature within range. The creature must succeed on a Wisdom saving throw.² On a failed save, the affected creature forgets one spell from their spell list of a level lower than the spell slot used to cast this spell (cantrips count as level 0). You may choose which spell is forgotten.³

When you cast this spell using a spell slot of 3rd or higher, you cause the target to forget another spell for every two slot levels above 1st.⁴

If the targeted creature is currently under the effect of this spell, its previously-forgotten spells are restored to its memory (unless chosen again).

This effect lasts until until the affected creature completes a long rest.⁵

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Specific Comments

I've provided footnotes at each point wherein I have comments on the spell:

1. The spell's duration is a bit unusual, but in general, as written, lasts until the end of the creature's next long rest. I would note, this is a very long time, which is unusual for a 1st level spell and is potentially an unbalancing element for it. The Warlock's Hex will only last a full 24 hours with a 5th level spell slot. I would recommend consider tying the duration to the spell slot and probably start with something like 1 hour.

   I noted that this spell does not require Concentration to maintain the effect. This also gives it a lot more power than perhaps initially intended. As the presumed purpose of this spell is to shutdown an enemy caster, I think it needs to be balanced by including the Concentration mechanic as this is typically the balancing mechanic for spells that shutdown an opponent. The spell has an inherent ability to shutdown an enemy caster by taking away their attack cantrip, which for low level creatures can force them to using daggers or unarmed strikes or can have a serious impact on certain legendary creatures whose legendary actions are tied to their cantrips.

2. Your original description indicated that the Wisdom saving throw was equal to the caster's spell save DC. This is unnecessary language; all spells use the caster's save DC unless they specifically say they don't.

3. This seems very powerful. As written, it can be inferred that the caster gets to view the full spell list of the target. You may wish to use language that constrains the information provided to the caster to only what they can cause to be forgotten.

4. Your original description stated 'each second level after 1st'. I was unclear if the intent was an additional spell for each spell slot above 1st or for every 2 spell slots above first. Regardless, for balance reasons I would recommend using the latter otherwise the caster of this spell is likely to completely shut down an enemy caster with a single upcasting of this spell that takes away nearly half of the enemy's spell list.

5. Your original language indicated that this effect lasts until dispelled or the creature completes a long rest. I don't think the language regarding being dispelled needs to be included as that is true of any long-term magical effect.

Answer 2

Let's go through the things you should look out for one by one.

1. Duration

The duration you list is rather unique, for a 5e spell. I believe you could avoid trouble by making it last for a fixed duration of 1 minute, 10 minutes or 1 hour. Also, instead of the 1/target limitation, consider making this require concentration, as it is a more widely used restriction which could serve the same purpose (although with slightly different results). In general, inventing as few new mechanics as possible is a generally good idea, as it will blend into the existing rules more seamlessly.

2. Known vs. prepared

Different classes are limited in the spells they can use in different ways. The most relevant distinction in this case is whether the target prepares their spells (like a wizard) or knows them (like a sorcerer). Unless the lore of your world dictates otherwise, the spell could effect either type of caster, but this will have to be included in the wording. This is also another opportunity to limit the spell, if you feel it is necessary. You could make two separate spells that could each target only one type of caster, for example. This could also be done with the arcane/divine distinction.

3. Do you know their spells?

As it is now written, the spell does not grant the caster the knowledge of which spells they could choose. I believe that should remain so and should be explicitly stated. This would mean that proper preparation and foreknowledge of the enemy would be even more valuable for a caster with this spell. Also that kind of information can be really valuable and should not be treated as a mere side effect of a spell (especially if you want to make it low level).

4. Cantrips

While cantrips are treated as level 0 spells in many cases, they often have more utility than 1st level spells, due to the fact that they can be cast at will. Especially against low level casters, "blocking" a cantrip this way can be devastating. The "cleanest" solution would be to not allow the spell to affect cantrips. If you wish to keep this capability, I would recommend either raising the base level of the spell, or the level at which it can affect cantrips.

5. Level

Now, this is often a difficult subject. In the previous paragraphs, I have outlined some ways you can tweak the power level of this spell. You will have to decide on these parameters depending on what place this spell will take in your world. Only then can you assign a level to it. If you limit it as much as possible according to my advice (1min, concentration, can only affect either prepared or known spells, cannot affect cantrips, confers no knowledge of possible choices) I believe this could stay at 1st level. On the other hand, if you leave it unrestrained, this could rise to level 5 easily, especially if you keep the duration as it is.

6. Access

You will also have to decide which classes get access to the spell. You will have to make the choice based on lore and your campaign. Still you should be cautious if you plan to place it on the spell list of a class that prepares from their whole list (like a cleric), as then all creatures with levels in that class will be able to prepare it in your world. You might even choose to make it a "restricted" or "secret" spell that is not generally available, but can be learned as a quest reward for example. This works best for wizard spells (as a method of gaining new ones is already there), but can be done for other classes too.

Answer 3

Very overpowered

Firstly the wording

Others have made some good comments on fixing it, but frankly unless you are publishing via DMSGuild or similar I find it enough to have the players understand it, and I don't worry about getting things to match the 'official' language, so maybe don't sweat the details is my advice here.

Onto the power itself

I find myself comparing this to several spells:

1. Encode Thoughts (A cantrip I only just discovered)
2. Detect Thoughts (A level 2 spell)
3. Modify Memory (A level 5 spell)

None of these are combat spells really, and the only one that talks about use in combat is Modify Memory, which gives advantage on any save in combat.

Modify Memory is also the only spell (That I am aware of) that allows you to cause another creature to forget something.

You have effectively weaponised Modify Memory, and even once fixed by way of concentration etc I would think this needs to be level 5+.

Finally

I would not allow this at my table for thematic reasons, even if it was fixed. It just doesn't mesh with the established style imho.

Answer 4

Overpowered

This spell seems combine some existing similar mechanics across other spells and abilities, but provides that at a much lower level with much more impact.

Overall, the options for stopping/interrupting spell effects are few and are only available under specific circumstances.

3rd level spells of similar capability

The spells dispel magic and counterspell are two options that allow a caster to either end a spell's effect or to prevent the spell happening at all.

Counterspell is the most similar in that you can use your reaction to counter any spell cast within 30'. You are limited for a guaranteed counter by the spell level and must succeed on an ability check for spells of a higher level. There's a good balance here of utilizing a reaction and a scaling of difficulty if you aren't using an equal or higher spell slot.

Dispel Magic doubles the range, but the balance here is that the spell has already been successful on it's target or area. You're having to wait until your turn in order to end it.

Thoughtseize has a closer range which increases caster danger, but you are preemptively countering a spell for the entire encounter/day. That's HUGE. Not only that, but you're still bundling a detect thoughts type spell into the mix by granting knowledge of what spells the caster knows in order to remove something from their list.

Arcane Trickster's Spell Thief ability

Another somewhat similar ability is that of the 17th level Arcane Trickster.

Immediately after a creature casts a spell that targets you or includes you in its area of effect, you can use your reaction to force the creature to make a saving throw with its spellcasting ability modifier. The DC equals your spell save DC. On a failed save, you negate the spell’s effect against you, and you steal the knowledge of the spell if it is at least 1st level and of a level you can cast (it doesn’t need to be a wizard spell). For the next 8 hours, you know the spell and can cast it using your spell slots. The creature can’t cast that spell until the 8 hours have passed.

There are a lot of similarities here in that the target loses the ability to cast the spell for 8 hours, but you also gain the ability to cast it.

Considerations for changes

I'd strongly consider this starting off as a 3rd level spell at a minimum to match that of dispel magic or counterspell. You'd also need to work on a method that brings it either more in-line with those spells or vastly increase it's spell level to be similar to that of the ROgue's ability. However, it's always risky to introduce a mechanic that's unlocked late game to other classes at a lower level.

While it's totally legit, I can tell you how frustrating it was to be a Paladin and have to wait for destructive wave while bards and storm clerics got it much earlier.

Answer 5

Some problems, linguistically and otherwise, in no particular order:

• The spell assumes you are targeting a character with a spell list
  • Many creatures don't have spell lists. What happens when one targets such a creature with this spell?
• The spell assumes that spells are on spell lists that a creature has, and each creature has one such list
  • Many creatures have spells that are not on any of their spell lists. Many creatures have more than one spell list. What happens in these cases?

• The spell assumes removing a spell from a creature's spell list matters

  • In general, the only times a character cares if a spell is on their spell list is when they prepare said spell (if they are any non-wizard prepared caster) or when they learn said spell (if they only know a limited number of spells). Notably, losing a spell from your spell list in no way interferes with casting that spell-- you will either still know it or still have it prepared or both, as fits your class. No class both cares about preparation and can prepare spells with a short rest, so the only way this spell affects a creature is that the next time they prepare spells-- if they are a prepared caster-- they can't re-prepare the selected spell. A caster that knows them would instead/also be unable to learn the chosen spell if they levelled up or otherwise had the option to learn a new spell before the end of their next long rest. So that's both extremely weak in PC hands and extremely jank when preventing level-up choices due to precise timing against PCs.

• The spell is overly verbose in a weird way

  • The spell specifies that the spell's save DC is your spell save DC, for example, which is completely unnecessary. It also says it 'lasts until dispelled, or' but all spells 'last until dispelled, or'-- that's kind of what 'being dispelled' means.

• The spell is self-defeating

  • Any caster who has access to this spell can undo the effects of the spell by casting this spell on themselves with a 1st level spell slot and choosing to lose a cantrip they already have, because doing so undoes each previous casting.

• The spell assumes affecting cantrips does something

  • Even more so than regular spells, cantrips don't need to be on your spell list. You only care about that when you gain cantrips, which is at level 1 and then a couple of times after that while leveling up, maybe. Even Magic Initiate, the most frequently available source of cantrips over the various level transitions, is unaffected by this, since it typically is used to give you spells off of someone else's spell list.

• The spell is unclear as to what "you may choose" means

  • The spell says you may choose the spell to be forgotten, but it is unclear if you get to know what spell list(s) a creature has/uses/used before making that choice. If you don't get to know for free, it's unclear what happens when you make an invalid choice. If you do, that's weird and could slow down the game if a creature has an unusual spell list.

• The spell is unclear because the system is unclear as to what spells are on what list for who

  • If you are a divine soul sorcerer, you might know some unusual spells, and they 'are sorcerer spells for you'. Many other features use similar language. If a creature has such a feature, are those spells 'from their spell list' or not? If not, what if the caster has such a feature and otherwise shares a spell list with the subject?

• The spell assumes all casters have cantrips

  • Many creatures that do have spell lists don't get cantrips. The spell is a 1st level spell, so what happens when you cast it on a creature at its default level and they do have a spell list, but they have no spells lower than yours in level?

• The spell has you target spell list entries in a way you don't seem to correctly comprehend

  • While on this point the spell is quite clear, your comments make it seem like you think the spell works differently. It doesn't target spells the subject actually has access to; it actually targets any spell you want within the level restriction that is 'from their spell list'. For example, you could cause a 1st level Wizard to lose access to Antimagic Field: Antimagic Field is on the Wizard spell list, their spell list, even if they can't cast or learn or prepare it.

Answer 6

Having the ability to know the entire enemy spell list is, I believe, far too much. That flavor of mind reading/control appears around ( I believe, can't check right now ) at 6th level spells or so.

Also note that mechanically in mtg Thoughtseize is a card that loses value as game goes by ( because generally your opponent has less cards in hand ) and it costs you 2 life. About the same amount of damage a 1 mana shock would cause you.

A way to make it more balanced would be to restrict the number of spells the caster gets to "see", for instance a 5th level thoughtseize grants a list of 5 spells from 0-4th level to remove from the target.

Adding a punishment to the spell would also go into the flavor and help balance things a little, such as taking a 1d4-2 +2/spell lvl past lvl1 in case target resists. There is little point using it on non casters and those have naturally decent resistance to mind effects, making it a more double sword than it currently is.

for instance that card against an aggro deck has a decent amount of chance of dealing you the same damage the card you took away would deal to you anyway.