Do we have to stick to the confines of a Multiattack description?

Question

If a creature has Multiattack that says

1 spear attack and 1 longsword attack

am I limited to just that? Or is this just some template where we can substitute 1 attack for something else, like

• 2 spear attacks
• a spear attack and an attempt to disarm?

Alternatively can I just substitute a spear attack for another sword attack? I feel being limited by number is a balance thing but by attack types made seems different.

For some creatures (like a Roper), making the attacks in that order make sense (Multiple attacks to try grapple someone so it can constantly attack them), but for something a bit more sentient (like a Goliath Warrior), it reads they make

2 Greatsword attacks or 2 Javelin Attacks

is that the limitation or can that be mixed and matched? Greatsword the warrior then javelin the spellcaster?

Answer 1

If you modify Multiattack you need to be mindful of balance

Generally the indicated CR for a creature is for playing the monster exactly as it is presented. This also means using Multiattack exactly as it is written. However, you can easily change a Monster stat block so long as you pay attention to any changes that would modify the CR.

Changing damage types is typically unproblematic. So is mixing melee and ranged attacks (I always do this). You have to be mindful if attacks have different damage output. For example check the Dragon Turtle:

The Dragon Turtle makes three Attacks: One with its bite and two with its claws. It can make one tail attack in place of its two claw attacks.

Bite is 26 damage, Claw is 16 and Tail is 26 plus Knockback. You could change some things here without changing balance too much, like exchange Bite for Tail (Knockback is typically a minor difference) but not others like exchange Claw for another Bite because one is 16 damage and one is 26.

Tl;Dr: As GM you can change Multiattack however you like but if you do you you need to check if the CR changes.

Answer 2

I don't believe there is much written in the rules about this, and I think there are two levels to it:

1. Can you use same rules as PCs when substituting shoves and grabs for regular attacks in a monster's multi-attack block?
2. Can you freely mix components of multi-attacks for monsters in situations where player characters might?

In brief, I think that a yes answer to 1 is more reasonable than a yes answer to 2. But the answer to both depends on how strictly you want to play to RAW, and the role the monster is playing in the combat.

Generally, monster stat blocks are simpler than PC stat blocks for good reasons. One reason is that the DM can do without the cognitive load of making loads of decisions for NPCs. Another is that flexibility is power, in that being more flexible in combat can makes an adversary more of a challenge to fight.

I think that, by strict RAW you are not given much guidance on how flexibly you as DM can interpret monster actions. It is reasonable to follow "there's no rule that says you can do that" for substitute actions monster multi-attacks, and claim that the RAW is use a multi-attack action as written, or use basic actions as per the PHB. Another Q&A on this site backs this up: Can monsters with multiattack take grapple and shove actions?

However, if I was using a monster with multi-attack as a major opponent, in a key battle, then I would likely use interpretation 1 above - allowing a monster that is described as competent fighter to substitute one of its multi-attacks for a shove or grapple as appropriate, much the same as a player character fighter, ranger or paladin could.

Saying "yes" to mixing and matching multi-attack components, as in your suggestion of 1 ranged plus one melee attack, is closer to homebrew (as in you could always homebrew a monster where it was the same as another one but with more flexibility written into the multi-attack, and some monsters already have that). You can justify it in the fiction, and against similar PC rules if you wish, but I would suggest save it for when the monster is being more like a boss monster. For two reasons - it takes more of your effort to decide the combination to use, and the flexibility you have added makes the monster more of a handful for a group of PCs than it would be as written with a strict reading of the monster's options.

Answer 3

Presumably, the multi-attack with different weapons means that the creature is actually holding those weapons and is using them to fight. Thus, if circumstances conspire to have the creature hold different weapons, then by all means, vary their weapon attacks. (Although, do be careful with the CR, as mentioned by @Anagkai)

Making two attacks with the spear and zero with the longsword, however, seems to go against the spirit of the creature's mechanics. There is such a thing as a fighting style, and that's what comes described in the multiattack entry. The "sentience" of the creature has little bearing on the issue.

Your example of the goliath warrior is pertinent. It makes two attacks with whichever weapon it happens to be favoring (or even holding) on that turn. As such, mixing weapons in the same turn seems to go against the description of how the creature fights. (Also, being able to engage the fighter with the melee weapon at the same time as the caster with the ranged weapon gives the creature a significant tactical advantage.)

The part about substituting one specific attack with other types of "attacks" is even more troublesome. Some of those "attacks" are actually actions, and if the creature even has the ability, they would come at the cost of all the attacks in the multiattack, not just one. Some others are substitutes for a single weapon attack, and in that case, I guess it could work, but you still have to consider whether the creature would even have the appropriate skill to attempt it, which is something that would appear in the stat block, I think.

For all of the above, I would caution against making these kinds of changes.

That said, as DM, when I want to introduce some spiciness in a combat and maybe catch the players off-guard, I have been known to introduce these surprises here and there, with the caveat that I allow them for only one specific individual, and I always point out a specific different description for that individual. If the change is harsh enough (like a significantly different damage or tactical potential), I also up the CR a bit for that individual.