How to obfuscate an enemy caster concentrating a spell in a group of enemy casters?

Question

My players face a cult of mages in a ruin. All cult members wear identical robes and conceal their faces with masks.

One of the PCs is a fighter and has shown to be particularly effective as dispatching other mages in the field, so this group of mages will try to disable him from combat via casting Heat Metal, then the rest of the mages will protect this mage until the fighter is disabled.

My question is twofold: mundane effects to obfuscate the caster and magical effects to obfuscate the caster.

1. What mundane things could be done to hide the caster?

Since all the mages are identical in appearance, I believe if they all perform the verbal and somatic components in unison the PC wouldn't know which caster to focus.

2. Are there any magical effects that could conceal the caster?

Invisibility cast by a second wizard on the primary after Heat Metal is cast could work. Minor Illusion could break line of sight to prevent ranged attacked.

Answer 1

Abuse the Ready Action

All the mages can perform their specific spell somatics and verbal components outside the view of the party. Then when the target comes into view, they release the effect.

Or they can release the effects when the last mage has completed their spell, not directly tying a spell to a mage unless the party can explicitly identify the spell being cast on their turn (usually requires some Arcane knowledge check).

Subtle Spell Metamagic

Your casters can also have access to the Subtle Spell sorcerers metamagic ability. This would eliminate the verbal and somatic components and make it much harder to identify what the mage is casting.

Answer 2

Why fake it? Have several of them cast Heat metal.

If they really want this fighter out of the fight, and if any of them can cast Heat Metal, have 2 or 3 of them cast it on the fighter's equipment. They could all cast it on his armor, or they could split their castings between armor, sword, shield, etc. Either way, there's no way to tell which one mage cast the spell, because several of them cast it. You're already considering having another mage cast Invisibility on the caster of Heat Metal, so you may as well use that same 2nd level spell slot to cast an additional Heat Metal spell.

Note: I'm not exactly sure how multiple castings of Heat Metal on the same object stack. See this other question. But regardless, if multiple mages cast the spell on the fighter's armor, that means he'll be suffering the effects of the spell until he breaks all of their concentration.

If you really want to hide the caster, use Greater Invisibility

If your mages have 4th level spells, one of them (let's call him Gary) can cast Greater Invisibility on another (let's call him Harry), who then casts Heat Metal on the fighter. Harry will not be hidden on the turn he casts the spell, but he will remain invisible, and on subsequent turns he will be able to take the Hide action while using his bonus action to deal damage to the fighter, and he will be able to leave the fighter's reach without provoking opportunity attacks. The fighter will have several options: try and track down the invisible Harry, try to break Gary's concentration to end the Greater Invisibility spell, or rely on support from the casters in his party to dispel one or both of the spells.

Answer 3

I'll start with a question:

Does the fighter know how a wizard casting Heat metal looks like?

Especially in the heat of battle (pun intended!). Is he relying on a fellow wizard telling him? Does he roll his own arcana test? What are the general rules at your table about this? Bytheway, wizards should not be able to cast Heat metal.

What mundane things could be done to hide the caster?

1. Steam to confuse (but not block) sight (i.e. the somatic component).
2. Gongs or bells to cover sounds (i.e. the verbal component).
3. Have other wizards carry iron or flames (i.e. the material components).
4. Have more than one caster cast Heat metal if that is so important!
5. Hide the caster behind some sort of screen where he can easily see the target but not otherwise.

Are there any magical effects that could conceal the caster?

Other than the spells you have already mentioned, other wizards can create illusions of casters casting Heat metal.

Concluding

Any solution you pick, it should not look like "You have zero chance to identify the caster because I create a PC-proof plan!". Let the party still have room to succeed if they come up with a smart plan.

Answer 4

Have all casters cast their spells at the same time, then avoid casting additional concentration spells

The big problem with hiding a spellcaster with a spell like Heat Metal is a combination of two things:

1. Casting the spell is generally obvious (it has verbal and somatic components)
2. The effect of the spell is immediate and obvious

If the spellcasters all ready spellcasting actions contingent on the last of them casting a spell, then all spells would be cast "at once" and it would be far from obvious which enemy cast which spell. Not casting additional concentration spells would prevent the target from deducing which of them must be maintaining Heat Metal.

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Cast from one or more obscured locations

If their dreaded enemy is a highly capable fighter, it's unlikely these spellcasters would rush out to open ground and start fighting them. They can make use of terrain features like cover and concealment to make them harder to see, which could possibly obscure what they're doing. Sequential turn resolution destroys this, but that's not information that would be available to characters in the game.

Spellcasters can dart in and out of cover, use the Hide action, and similar to obscure what they're doing.

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The shell game

There's a long-standing con in which players try to guess which shell (or cup, or whatever) is covering a pea (or something like that). The shells are moved around in an effort to distract the player such that they cannot track which shell covered the pea initially, making it hard to identify the correct shell. In real life, this is nearly always a scam (the pea is removed from the table).

But in your game the spellcasters could run out of sight, and if they all look the same as one another that would be enough to hide which one is maintaining the spell, whether or not the fighter identified them correctly in the first place.

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Use magic items which cast Heat Metal

Depending on what skills and resources your spellcasters have access to, they could obtain or produce wands which cast Heat Metal. Doing so could go a long way towards hiding the caster, as the normal somatic and verbal elements would not happen. The wand could even be passed around, further obscuring which person cast the spell, and allowing fresh castings when necessary.

Having multiple wands, or some decoy wands, can combine this with the shell game approach.

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Illusions

Illusory decoy casters would make it harder to identify the correct target, even if the fighter knows which enemy initially cast the spell. These would have to be created and maintained by others, but since they are on hand anyways that's not a tall order. An extension of this could be granting invisibility to the one casting Heat Metal after they've cast the spell, via a spell maintained by someone else or a magic item, and would make them very difficult to locate.

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Multiclassing and feats

With levels in Sorcerer, your casters can take the Subtle Spell metamagic feat and cast spells far less conspicuously than normal.