On our last game, a little incoherence happened in the middle of a fight.
I threw an Acid Arrow to a caster, which was threatened by our ranger and fighter in melee (yup very bad position).
So naturally, the DM goes for Defensive Casting; Concentration 15+2x spell levels. Which is, in my opinion, really to easy on reaching lvl5-6. Anyway.
But as he does defensive casting, he also suffer continual damage from acid arrow.
Would he simply have to do two separate easy concentration check (one at like 14 and another may be 19, while having +14 concentration from lvl6 + 4 int + 4 combat casting), or a single, harder concentration check?
Also, am I the only one who thinks concentration checks are WAY to easy? I find a bit special that casting while jumping of a cliff with three acid arrow is such an easy deal, and should be, in my view, nearly impossible and heroic act.
It should be two checks. Each one is for a different thing.
Agreed, two checks required. One with a static DC to not lose the spell while casting it defensively and another with a variable DC based on damage taken during the casting. If the caster was on a heaving ship in the middle of a storm, I'd potentially call for another couple checks.
Note: Combat Casting doesn't help with any type of concentration check except to avoid provoking AoO. So the caster would only be +10 at 6th level against the damage. So average of 20 with a DC of 10 + 1/2 damage taken.
I'd say that using acid arrow on a 6th level caster thinking that's a way to stop him from casting is the problem. Instead, ready an action to cast something at him. Heck, even if acid arrow is all you have, ready the casting so the DC is 10 + damage. 15 is better than 12.5 since you'd be talking about a 25% failure rate instead of a 10% failure rate.