Untitled Trigger 001
Unit - A unit Starts the effect of an ability
(Ability being cast) Equal to Breath of Fire
Unit Group - Pick every unit in (Units in (Region centered at (Position of (Triggering unit)) with size (1000.00, 1000.00))) and do (Actions)
Loop - Actions
If (All Conditions are True) then do (Then Actions) else do (Else Actions)
If - Conditions
((Matching unit) has buff Breath of Fire) Equal to True
Then - Actions
Unit - Cause (Triggering unit) to damage (Matching unit), dealing (Real((Strength of (Triggering unit) (Include bonuses)))) damage of attack type Spells and damage type Normal
Unit - Remove Breath of Fire buff from (Triggering unit)
Else - Actions
Well, swap "Begins casting" with "Finishes casting" and it might work. You could also have a different buff for each level of BoF.
And besides, what're the odds that two people are going to be casting a particular spell so close to each other that the trigger can't keep up with it? They'd have to use it at EXACTLY the same time. And even then it's unlikely.