Quote Originally Posted by Unoriginal View Post
How about:

Player: "I cast Fireball".

DM: "OK. The enemy caster didn't think you could cast another spell that powerful, so he doesn't counterspell it/the enemy caster was worried about you powers given your last spells, and tries to counterspell this one."
Yeah, pretty much. I plan out general tactics for my complex monsters, and if it comes down to it I'll do something like this:

Flaw: Arrogant, so never Counterspells the first spell cast against them
Above 50% hit points, Counterspells 11-20
Below 50% hit points, Counterspells on 6-20
If more than one spellcaster, always Counterspells the Arcane caster

And just roll every time.

It took a minute, and now I can say those out to the players, roll in the dice tray in the middle of the table, and it's now a mechanic instead of the stuff most of you are terrifying yourself / complaining about