Imaculata
Hero
Once in a very hard fight, we had the situation that our wizard was out of spells and all down besides the BBEG and our ranger. The ranger shot the BBEG and left him standing with 2 hp or so. The retaliation downed the ranger and the wizard, without weapons threw the lamp he was carrying and could only hit with a 20. And he rolled a 20 in the open. The most awesome ending ever.
Now imagine that exact same scenario, only after being hit by the lamp the big bad still has 1 hp remaining... why would you simply not let the creature die at that point?