What are the downsides to multi-classing?

Question

I've been having a discussion with my players recently about the game we're running, and am having trouble answering a question that was posed to me.

Why would you ever NOT multi-class in D&D5e, assuming the option to was available to you?

For instance, we have a 3rd-level Barbarian who has started multi-classing in to Druid. He's not going to be getting any more significant Barbarian abilities until 9th-level, so why not gain the ability to cast healing spells on himself, or shapeshift in to a bear whilst raging?

Or a 3rd-level Warlock; what are the downsides to multi-classing in to Rogue (Assassin), so that you can cast and see through magical darkness whilst using the assassinate ability?

The PHB says:

you'll sacrifice some focus in exchange for versatility

but unless you're very strict character roleplayers, I can't see that much focus really being sacrificed. It seems like the phrase "A jack of all trades, a master of none" doesn't seem to apply in this instance; you really can become "a master of all trades".

A thorough answer to this would be appreciated, else I can see my group becoming barbarian-druid-warlock-paladins sooner rather than later.

Answer 1

There are two main downsides to multiclassing, though depending on your play style and group you may never run into the lesser of the two issues.

Falling behind single-class characters

The primary issue, and one that is more likely to impact any game that makes it past 5 levels or so, is that classes scale in power generally at the same time. Casters get level 3 spells (Fireball, et al) at 5th level, martial characters get Extra Attack at 5th level, and Rogue and Bard get Uncanny Dodge/Font of Inspiration.

If you're a wizard and you decide to multiclass into rogue before or at your fifth character level, you will forever be a level behind in your spell progression, and since Challenge Ratings take into account your character level and expect that a level 5 character will have either Extra Attacks or fireball (or other equally powerful spells), your character may have a hard time keeping up damage-wise in combat situations, because you're only a character with level 4 wizard capabilities and level 1 rogue capabilities, neither of which are very impressive compared to what you get at 5th level with either. The only thing you do gain at that point is an increase in your proficiency from +2 to +3, which isn't nearly enough to make up for the initial delay in spell/class feature progression.

Now, it is true that this impacts spellcasters significantly more than it does martial characters, but it does affect your wizard's ability to be the best wizard he can be.

A note on ability score improvements

It is also important to note here that unlike in previous editions, 5th edition D&D ability score improvements are granted by class level, not character level. This means that multiclassing into more than one class can and likely will result in suboptimal ability scores at higher character levels, but when advancing through the tiers of gameplay this effect can be more substantial.

More on ability scores

The multiclass rules (if you choose to use them) require secondary (and tertiary) classes to meet certain ability score requirements. If those requirements are ignored, it is likely that those class levels will be "wasted" as the character will display subpar performance in that class due to their inability to keep up with characters of a similar level. This is less of a problem in 5e due to bounded accuracy, but is still probably enough of a deterrent to multiclassing into more than two classes.

No capstone abilities

The second real drawback to multiclassing, which I mentioned may not affect you based on your group and play style, is that levels are capped at 20 in 5th edition D&D, meaning that characters who multiclass won't ever get their capstone abilities (and possibly 17th/18th/19th level abilities). Once you reach level 20, you can gain no more class levels and thus you can not gain any more class features. Since most games don't reach this level of play, it's not as much of an issue, but is something to consider, especially if starting a game at high level with the intent to play at level 20.

Examples

Using your example of barbarian-druid-warlock-paladins, that's a character that's going to need at least a 13 in STR, CON, WIS and CHA. Unless your player rolled really well it is unlikely they have a character build that can even support this, especially given that the character will likely miss out on one or more ability score improvement throughout her life.

Imagine this theoretical character: barbarian 4/druid 4/warlock 4/paladin 4. This character has a proficiency bonus of +5, and has received 4 ASI's throughout his career.* However, his class features for any given class only equal that of a level 4 character. He is tier 1 in every class, and has no tier 2 abilities that can help his survivability or damage output in higher tier gameplay. He is in a party of APL 16, with 3 single-class characters and the party is facing a CR 16 monster. Which party member is going to be the least helpful in this situation at a high level of play? Probably the character who has only one attack per turn, no access to anything above a level 2 spell, and no ability to wild shape into anything but a 1/2 CR beast that can't even fly.

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* Note that this is on par with a single-classed wizard character; however, a level 16 wizard at this point has access to many spells (up to 8th level) that can enhance his abilities and defenses that the multiclassed character does not have access to.

Answer 2

For instance, we have a 3rd-level Barbarian who has started multi-classing into Druid. He's not going to be getting any more significant Barbarian abilities until 9th-level...

I would strongly disagree with you on that statement.

At 4th level, your barbarian receives an Ability Score Improvement, which is essentially a +1 to every single task that uses a single ability score. He can hit harder, he's harder to hit, he's got more HP...in 5th edition, getting that bonus is huge, because there's not a whole lot of other ways to permanently or semi-permanently augment your attack rolls/skills/saving throws/etc.

At 5th level, your barbarian receives Extra Attack. This is huge. In past editions, you could multiclass between different martial classes and still receive additional attacks. This is not the case in 5e; if you multi-classed into Fighter from Barbarian level 4, you would have to take 5 levels of Fighter to get to Extra Attack 1.

At 6th level, you get a feature from your archetype. Granted, the Totem features at this level are non-combat oriented, but that's no reason not to take them if you chose the Totem barbarian. D&D can present all sorts of challenges, from killing a dragon to take its loot to persuading a dragon to part with its loot to sneaking into the back door of a dragon's lair and taking its loot, and being able to kick down the door or shove aside the boulder a villain throws in your path as they escape, being able to remember or recognize said fleeing villain's face from 1 mile away, or being able to track and overtake said fleeing villain without tiring yourself out or losing his trail is not a dead level at all (and if your barbarian is a Berserker...congratulations! He can no longer be charmed or frightened, which means while the sylphs are dominating your party members or the red dragon is causing them to cower in a corner, you can just walk up to the scary monster and keep swinging your sword).

At 7th level, you get two VERY powerful features. First, you have advantage on initiative rolls, which means you can take down key threats quicker or just remove a few mooks that would otherwise be giving the party trouble. Second, you can't be surprised. Ever. As long as you aren't sleeping on the job or magically frozen in place, no one can ever ambush you.

8th level presents the same benefits as 4th, so I won't cover them.

If your barbarian wants to gain access to some spellcasting, I would recommend the Magic Initiate feat (though the feat becomes less useful when you realize you can't cast the spells you've learned through it while raging) or the Ritual Caster feat. As for wild-shaping, a 2-level dip into Moon Druid wouldn't be completely out of line for a barbarian. Just keep in mind that you can't use your own physical stats while wild shaped.

The 3rd level warlock you mentioned has to go through 3 levels of rogue to get that Assassinate ability. Which means that they're losing out on additional invocations and spells compared to a straight warlock. Bestow Curse is a fair bit more powerful than Hex.

The PHB says:

you'll sacrifice some focus in exchange for versatility

That statement does not refer to roleplaying. A 5th level wizard can deal 16d6 fire damage in the space of 2 rounds thanks to Fireball. A 5th level barbarian can deal 4d12+24 slashing damage in the same timeframe. A Barbarian 3/Wizard 2 can do neither of those things, and even a Barbarian 5/Wizard 5 can't do them both at the same time.

Answer 3

It takes a lot of time and effort to do it properly

It is difficult to mess up a single-class character¹ but multiclassing efficiently is hard.

You have to keep in mind what features can be fueled by another class's resources (you can use Sorcerer spell slots for Divine Smite) and what not (Eldritch Strike only works with Warlock slots), what weaknesses can be overcome by multiclassing (Wizards can cast in Plate if proficient) and what not (Barbarians don't benefit from rage in Plate, even with proficiency).

You don't have to learn everything by heart, you can read the excellent guides out there, but that, again, takes a lot of time.

With careful planning, the downsides are negligible compared to the benefits

Some of the costs you might pay anyway (Ability Scores), and some are less important than they seem at first.

Capstones

I have been playing some version of DnD since 1993, my highest level character was 15. Either a TPK forced a new start, or too many participants lost interest, and the game just died away.
Even if you reach level 20, it is just 5% of your career, how could a capstone compete with Full Plate and a Shield for 19 levels?

Compare every level

Someone mentioned in one of the comments that while the +1d6 from Sneak Attack helped a lot his Fighter/Rogue in low levels, it was painful to watch how much stronger single-class characters were at level 5.
While this is to be expected, most likely he was stronger on levels 2-4, 6-10 and 12-19. So I would argue he was stronger overall. On those 3 levels hopefully the other players can help out, but this is the realm of party optimization.

Ability Scores

You must have 13 in both Dex and Wis to multiclass into Monk, but I think it is very hard to create a decent Druid without these anyway, so this is not an extra cost.
Of course a Paladin/Monk is harder to achieve, you need a 13 in Str, Dex, Wis and Cha, but it is far from a great idea anyway.

Spells

It is true you do not get higher level spells for a long time even if you multiclass into another prime caster. However, spell power is not linear with spell level.
In the 11th level party I play in the most used spells are:

• Faerie Fire (because the target does not get a new save at the end of its turn)
• Blindness (because no Concentration)
• Hold Person (because criticals for the whole party)
• Bless (because no save, so always works)

Focus vs Versatility

Saying multiclassing provides versatility at the cost of focus is overly simplistic, and plain false in most cases.

A bad workman always blames his tools

If your Paladin spends all his ASIs on Intelligence, and you end up with a weak character, the problem is not with the concept of ASIs.
If your Wizard takes all the feats in alphabetical order, feats in general are not at fault.
Similarly, you should not blame multiclassing if a Fighter 10/Wizard 10 is weaker than an Eldritch Knight 20. This is just bad design on your part, forgetting that level 11 is a big one for the Fighters. A F12/W8 would me much stronger.

It is entirely possible to become more focused by multiclassing:

• A Shield Master Fighter with one level of Rogue gets more out of the prone condition with Sneak Attack, and adding Expertise to Athletics makes him better at proning
• One level of Monk on a Moon Druid makes him better at Wild Shape, providing much needed AC to the beast forms (Unarmored Defense)
• Two levels of Paladin on a Moon Druid helps to spend the spell slots that would not see much use otherwise (Divine Smite)
• One or two levels of Fighter is a great addition for a Bladesinger, as Fighting Style, Second Wind and Action Surge can make you a better Warrior Mage

When to Multiclass

This depends heavily on the primary and secondary class, subclass and even on your Ability Scores.

When to stay:

• As others pointed out, level 5 is a big jump for most classes, (not so much for Bards, Rogues and Moon Druids)
• Ability Score Improvements (ASI) are very important, so try to reach level 4 or 8 in all your classes

When to leave:

• Extra Attack does not stack with itself, so take it only from one class. A Barbarian 4/Fighter 6 is significantly stronger than a 5/5 split
• Paladins get their arguably strongest feature on level 11, I'd stay one more for the ASI, but this is a very good place to get out
• Clerics get one of their best spells at level 7, stay one more for the ASI and the Domain feature, and switch to some other spellcaster for more spell slots or to a class with Extra Attack
• Warlocks learn a new spell every level up to 9, after that it is only once per two levels. Mystic Arcanum is also significantly weaker than getting new spell slots. Bladelocks might want to stay until level 12 for Lifedrinker, others should leave even sooner.

When to Dip

Many classes are front-loaded, meaning that some very good features are available at first or second level.
If you take so few from another class it is almost inconsequential when you do it, the most important thing to keep in mind you only get the saving throw proficiencies from your first class.

What to pick

• One level of Monk gives great Unarmored Defense for Druids and Clerics
• Two levels of Warlock gives a much needed powerful cantrip for Sorcerers and Bards (Eldritch Blast + Agonizing Blast)
• One level of Cleric gives casters Medium Armor Proficiency (possibly Heavy) and Domain features, with full spell progression
• Starting as Fighter gives casters Armor Proficiency and Constitution Save (and Second Wind)
• Two levels of Fighter provides the only way to cast two spells in one round (Action Surge)
• One level of Rogue gives you Expertise if you want to be really good in two Skills, and +1d6 damage with some very easy conditions
• Two levels of Rogue gives you great mobility for bonus actions

Biggest drawback: Time

Bookkeeping and careful planning takes a lot of time:

• I have a Bard2/Sorcerer4/Warlock5 character, keeping track of spells known is a real pain, I had to open a spreadsheet for it
• A friend really wanted to add a few levels of Rogue to his Ranger, but realised too late that it would need a 13 in Wisdom too

TL;DR It is possible to create multiclass characters that are ahead of single-class characters in power, versatility or both. It just takes several hours of careful research and planning.
Read the guides on giantitp.com or enworld.com.

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¹ Unless you create a Beast Master Ranger, or a Way of the Four Elements Monk.

Answer 4

I can see why there is some confusion on this. The multi-classing rules are clear, but require a pretty careful reading lest you miss some of the key drawbacks to multiclassing.

As Legendary Dude said, you will miss out on late-game abilities and the like because once you hit 20th level (overall, as a character), there's no more leveling. There are epic boons, but additional class features are effectively locked out.

This drawback applies to quite a few classes, all of whom have some pretty awesome capstones (i.e. Barbarians, Clerics, Druids, Fighters, Paladins, Rogues, Wizards). But there are intermediate abilities that remain locked out, until you reach the appropriate class level. Unlike in 3.5 where taking levels in 2 different classes that provided Uncanny Dodge automatically gave you Improved Uncanny Dodge, 5e rules function more along the lines of you either have it or you don't. So you either go 7 levels of Rogue or Monk for Evasion, or you don't get Evasion.

As it relates to casters, it's important to note that the highest spell level you can know and cast is dependent upon your level in the applicable class. The spell slots available continue to increase provided that both of your classes are primary casters. For example, a Wizard 3/Cleric 2 has 3rd level spell slots available for use, but they do not have any 3rd level spells. They only get to utilize that 3rd level slot for the 1st level spells that their Cleric levels give them or the 1st and 2nd level spells that their Wizard levels give them. In this way, they've traded raw power for versatility.

Lastly, it's important to remember that ASIs, and by association feats, are tied to class levels. You do not get an ASI because you reached 4th level as a character; you get it because you reached 4th level as a Rogue or a Wizard or another class. If you want to level-dip into a little bit of everything, it will be a very long time before you see an ASI.

Answer 5

I think this line points to a clear misunderstanding of the various classes:

He's not going to be getting any more significant Barbarian abilities until 9th-level, so why not gain the ability to cast healing spells on himself, or shapeshift in to a bear whilst raging?

5E is written in such a way that each level for each class is significant. There is "a thing" at each level, just look at that table at the front of each class description and you'll see something important happen for each level. In some cases, "the thing" might be as simple as access to spells of a new level, but that's very important for casters or an Ability Score Increase (ASI) / feat which is important for everybody.

It's really important to note that things like ASI's and second attack are all acquired based on Class level not Character level. Multiclass also limits the level of the spells you can know. So if you take Wizard 4/Cleric 4, you would have the same spells slots as Cleric 8, but you wouldn't know Fireball or Raise Dead.

Missing these things will severely impact your damage output and thus impact the effect you can have on combat. There are some multiclass combinations that can mitigate some of these effects, but it's hard.

Answer 6

The Pro: Versatility

Adding flavor to otherwise bland and dead-horse single-class archetypes aside, Multiclassing, especially dips for proficiencies or low-level archetype powers, offers you a great variety of unique skills, powers, and proficiencies to add to your personal portfolio. Feats (if allowed) are rare for most classes and having multiple class archetype powers can be very attractive for those willing to pay the price to not be Generic Rogue #9723558.

The Cons: Sacrificing Power

Every level you multiclass means lopping off potential powers reserved, or even expected of, mid and high level play. Each multiclassed level starts to cut off a casters' access to 9th level spells, and Clerics immediately lose the upgrade that allows Divine Intervention to work automatically. Front-line types also begin to sacrifice Hitpoints (and recovery die), unique features, and valuable ASI's by taking levels in classes with weaker hit dice.

Just as bad, the long term consequences of early-career multiclassing is delaying access of ASI's and mid-tier powers to progressively later stages. A 10/10 multiclassed cleric not only loses the divine intervention upgrade, but could delay obtaining divine intervention entirely until 19th or 20th level, and only in its weakest state. Such a character may not even play long enough to even see those levels or powers in play, while a pure class could have been using it for weeks or months to dramatic effect.

The Short Answer: Deep Multiclassing is bad

A 10/10 split is bad at best, and a horrible corner to paint yourself in at worst when you're facing would-be deities, high-end liches, and elder dragons and you're a cleric that can't even cast Heal, or a Sorcerer that can't upcast Counterspell to thwart a Disintigrate spell, or a scraggly fighter with a Wizards' hitpoint total. Over-diversifying can rapidly become a problem when you have too many options and only one turn in a round to use them.

Small dips of one level for some extra proficiencies or powers, up to third level for archetype powers, are often a best case scenario. This doesn't change that picking the class and archetype that fits what you want and staying single class is often the way to go. Fighter-Casters should go Eldritch Knight, Cleric-Sorcerers should pick Divine Soul, and would-be Cleric-Fighters are better served as War Clerics. Divine Souls may opt for levels of cleric for some precious extra spells, armor proficiencies, and some domain powers (plus more spells), but each level taken delays ASI's, availability of metamagic, and delays bloodline features.

5e has dramatically improved the flexibility within the classes, so it's best to find an archetype that fits what you want to do and stick with it. Arcane Tricksters, Eldritch Knights, Divine Soul Sorcerers, War-domain Clerics, Paladins, Rangers, and Hexblade Warlocks are essentially self-contained multiclasses.

If you are going to multiclass, the best way is to not do it early, or at all, until levels 9-11. This keeps your initial ASI's on track and builds a strong foundation of mid-tier powers before you start to dilute them.