well, a few battles ago, the PCs were up against a lich/archmage and I gave the lich a ring of positive energy protection that I completely forgot about... the party rogue flew above the lich & held his action. I figured he was going to try a sneak attack or similar once another party member closed. However, when the lich started casting (Otto's Irresistable Dance to target a party caster), he used his held action to pour a maximized potion of cure serious wounds onto the lich for 39 points of positive energy damage. So, the lich promptly failed its DC: 54 concentration check & lost the spell. It should have been zero points of damage and one party caster would have had to take their action to dispel the Otto's on the other caster. Instead, they both were able to target the lich with their own dispel magics and slowly debuff it...