Just a note in case anyone is worried I’m adding a mage to every encounter, I very rarely use counterspell against my players; it’s one of the spells I consider to have high “fun-ruining” potential.
I’m struggling a bit to decide on how to handle this interaction in a way that feels fair. From my understanding RAW, a character doesn’t know what spell is being cast. I think you can use your reaction to make an arcana check to discern it, but of course then you can’t counterspell it. For enemy spellcasters I generally describe what’s being cast, instead of naming the spell right away, but it can slow combat down, and is a bit one-sided since when a player casts a spell they lead with “I cast X”. This leads to an imbalance where I’m aware of what’s needed to counterspell something while the players are not, and can cause some awkwardness trying to decide how to play around that without metagaming.
I can think of a few different ways to handle this, each with its own drawbacks, but I’m curious to hear what y’all do at your tables!
This reminds me of an instance where my WM sorcerer counterspelled what I assessed to be a high-level spell, but then the bad guy counterspelled my counterspell and won. However, because we were playing with WM variant rules where the chance of it triggering are higher when higher level spells are used, a WM surge happened at that exact moment too and caused absolute mayhem.
A fun mechanic for spell casters to identify what is being used against them might be to have them automatically recognize any cantrips, or put it behind a low perception skill check, like DC 5 or 7, and increase the DC for every spell level or slot thereafter. In addition, the DC could be decreased by the highest level of spell known/available to that player.
This could be a special reaction only available to spellcasters that represents their instinctual familiarity with magic. I wouldn’t make it cost a reaction point, but I would limit its use to something like their proficiency bonus with a LR or SR recharge.
So, for instance, a BBEG casts disintegrate(lvl 5). A spell caster in the group uses this special reaction to recognize the spell, and knows one 4th level spell. DC would be DC = (5 + (2 * ESL)) - GSL, where ESL is “Evil Spell Level” and GSL is “Good Spell Level”. So being a lvl 5 spell, we would get:
DC = (5 + (2 * 5)) - 4
DC = (5 + 10) - 4
DC = 15 - 4
DC = 11
However, for that one dude in the party that took a multiclass level or two in warlock and would only know a lvl 1 spell, his DC would be 14.
Thats just my spitball answer though, but probably what I would start with.