There have been two so far in the game I'm running.
1) Ripclaw. Spends 5 rounds without landing a single hit before dying.
2) Bua Gorg. The cleric casts summon monster III, bringing forth two uncontrolled dretches. One casts stinking cloud on Bua, catching Drevoraz in the area. Both miss their saves and both are nauseated for 5 rounds after leaving the area. Both die before recovering.