Faking a spell in order to make an enemy caster waste a counterspell

Question

Wizards are smart and sorcerers are cunning, and their power is pretty directly tied to how many spell slots they have remaining. As such, losing one to a counterspell can turn the tides of a battle quickly.

Suppose a player wished to force an enemy spellcaster to use a precious counterspell slot while preserving their own slots. The envisioned use of this tactic is to sacrifice one action in order to allow another caster in the party to cast their own powerful spells without fear of being countered, prevent the mage from using their reaction for something such as shield, and the deceiver can conserve their own spell slots.

For the sake of argument, the enemy is not concerned with counterspelling cantrips, and will only counter a levelled spell that appears sufficiently dangerous (e.g. fireball) or other tactical spells (e.g. dimension door, healing, summoning)

I propose 3 options:

1: Deception (Intelligence) check to make convincing enough verbal/somatic components without actually accessing the weave for the spell, contested by an insight check on the enemy's part. Leaving out non-mechanical nuances such as 'can casters detect when the weave is accessed' and 'can you say and do the components of a spell without actually casting the spell', this is a pretty simple approach. The downside however, is that from a strictly RAW standpoint, the mage is not actually casting and is thus not a target for counterspell. RAI may differ however.

2: Similar to above, but requiring the casting of an illusion-based cantrip such as minor illusion or prestidigitation to mask their actions and give the appearance of their casting. This eliminates the issue of not having a valid target for counterspell, as a spell is indeed being cast. However, it would seem that the effects of such an illusion spell would take effect after it's casting, thus rendering the whole point moot; the enemy caster may recognize that they just cast a spell known to produce misleading effects*, using their action to do so, and likely cannot cast a second spell the same turn. (multiclassing or metamagic notwithstanding).

*There is a level of metagaming, since as a DM I have to know what spell is being cast by the players, and per Xanathars pg 85, identifying a spell takes a reaction.

3: Some sort of homebrew spell that acts as a magical trap, where it uses the verbal and somatic components of a different spell but with a very subtle additional difference (such as, say, fingers crossed behind your back!) that refunds the spell slot used if it is counterspelled, otherwise it uses the spellslot with no effects.

Which of these would you prefer at your own table, or if you have another option what might that be?

For those who say that you wouldn't allow it, keep in mind that (particularly options 1 and 2) it's likely to only work once or twice at most, and the enemy may be granted advantage on the insight and/or the player disadvantage on their roll for subsequent attempts to replicate diminishing returns on the tactic.

Answer 1

This is wrong:

the enemy is not concerned with counterspelling cantrips, and will only counter a levelled spell that appears sufficiently dangerous (e.g. fireball)

Rules As Written, the player begins by casting a spell, and the enemy caster can make a decision to counter that spell or not. The enemy caster does not have any information about what spell is being cast when they make their decision. The enemy caster could use their reaction to try to figure out what spell is being cast, but then they've lost the opportunity to counterspell.

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So, RAW, any cantrip will accomplish this effect.

If a character had no cantrips at all, and they wanted to spend an action on a bluff that they were casting a spell, I would allow a Deception check opposed by the NPC's Insight.

I believe it's unclear, Rules As Written, whether an attempt to counterspell a nonexistent spell would consume a spell slot. I would rule that it would.

Note that this still might not draw a counterspell from an NPC. That would depend on whether the NPC was intending to counterspell a specific PC, or simply to counterspell the first spell that was cast.

Answer 2

Can you identify a spell as it's being cast and then counter it?

Before we discuss the idea of faking, there's a prior question. Can you even identify a spell before countering? This is iffy and depends on the DM.

Officially, Xanathar's Guide says that "a character can use their reaction to identify a spell as it's being cast", with an Arcana check vs DC 15+spell level to correctly identify the spell. If you spend your reaction identifying a spell, you don't have a reaction to cast counterspell, so you can either identify the spell, but then be unable to do anything about it, or counterspell it blind, with no idea whether you're countering a fireball or an acid splash.

However, I and a lot of DMs (and the 5e-based PC game Solasta) make the two reactions part of the same reaction -- you roll to identify the spell (which coincidentally lets you know what the spell level is by knowing the DC you're rolling against), and pass or fail, you can then choose to attempt a counterspell on it.

This gives a player a decent amount of information to work with: If they succeed the check, then they know what the spell is and can decide whether it's worth blowing a 3rd level spell slot on; if they fail, they still at least know what the spell level was, which prevents wasting counterspells on cantrips.

Of course, that all depends on actually concealing the identity of the spell in the first place. In my games, I very rarely say anything like, "Okay, he's going to cast a spell, do you want to roll to identify it?" I usually just blurt out, "The evil cleric moves in front of the altar, lifts his arms, and casts flamestrike at you!" The cat's out of the bag by the time the sorcerer even has the option to jump in with "I cast counterspell!" So depending on your table, this may not even really come up as a question.

Okay, so can you fake-spellcast?

The rules don't give us an answer to this, but there's lots of things a player might attempt that the rules don't strictly allow (or disallow). As a DM, I think it's a fine plan. I like creative players, and spending an action doing nothing but pretending to spellcast in order to possibly trick an enemy into wasting magic is entirely balanced.

I'd allow a player to roll Deception or Performance to try to pull this off, opposed by the spellcaster's Arcana check. Heck, the person trying to pull this off doesn't even have to be a spellcaster -- I could totally see a Rogue mimicking the components of a fireball spell just to trick an enemy wizard into wasting his magic, at least provided there's a spellcaster with fireball in the party that he can watch and learn from. (It'll probably only work once, though it could be a funny gag to fake-cast once just so they'll decide not to counter it when you cast for real the second time...)

This may or may not make sense by the strictest possible reading of the rules-as-written, but I would argue it's absolutely how the game should be run: Players coming up with crazy strategies to solve problems is a core part of the game, and I never want to tell my players "no" if I can help it, especially when rolling with it will make a fun moment.

Answer 3

This isn't meant to be done - my primary two reasons follow.

1: Take careful note of the fact that the bit about Xanathar's that you referenced uses a reaction - counterspell already existed, and this was an intentional design decision. Unless you have the help of another party member with the appropriate skills using their reaction, by design you are meant to either know the spell being cast or counterspell it, not both. This limitation is what keeps casters without counterspell from being worthless in an encounter with one.

2: Detect thoughts allows the mage to counter what you're suggesting without giving them a free reaction, with no saving throw. The surface thoughts portion of the spell requires your action, is saveless, and is specified to be about what is immediately on their mind - you use your action to scan their thoughts (ostensibly, what spells they might cast next) and utilize the information to decide whether or not to counterspell. The enemy knows you're reading its thoughts, and can spend an action to try to end the effect with an intelligence check when you do this, but then you don't have to worry about counterspell that round in the first place... Using this on an illusion also reveals the ruse, since illusions don't have thoughts of their own.

If you're determined to go through with this

Option 1: Consider replacing the ability modifier for the skill check with the primary casting stat of the person being deceived- this gives them the advantage (without giving them Advantage) on a check that is, by its nature, designed to bait out an action based on the victim's knowledge, not the perpetrator's.

Option 2: A fair hand here, IMO, would be requiring the use of a major image spell to create a duplicate image of the caster constantly casting spells every round. An enemy mage has a good chance of beating this tactic in short order, but if the casting mage can break LoS the Major Image can't be counterspelled, and then utilizing movement tactics near the illusion afterwards can possibly cause the enemy to lose target lock of the real caster again.

Option 3: A game is meant to do whatever is fun- if your table finds this fun, go for it- but I encourage you to make this your last option. Creating a custom spell that works for a homebrew mechanic that specifically violates the action economy of mages to enhance/nerf counterspelling (depending on what side you're on) is a very, very slippery slope and could quickly have unforeseen consequences down the line.