In our last PF game, the group was facing a quasit/summoner with a nigh-unhittable AC, DR 5, fast healing and invisibility at will power. While it was doing relatively little damage, the party could sense this was going to be long, dragged-out fight.
During part of the fight, the party summoner's eidolon was hit with a fear spell from the quasit, and dismissed the eidolon rather than watch it go running down the halls. Partly by luck, he summoned a celestial war dog to replace it. Its scent ability helped track it down when the quasit went invisible, but there was still the problem of hitting, and by now the party's main fighter had been poisoned by the quasit.
The quasit had retreated into the air over a 3' deep pool in the room to avoid melee attacks when the party was hit by inspiration. The group's halfling successfully taunted the quasit to come after her, and, with the celestial dog 'pointing' out the quasit's location, they grappled the little beasty and pinned it under the pool, drowning the little hellion.
They were quite satisfied with their creative defeat of their enemy.