Skills that destroy corpses are helpful to employ around him, especially if they can be used from some distance, such as some of the Druid's Vines, or the Paladin's Redemption. Necromancers can have the most fun, fighting fire with fire by using their own Corpse Explosion skill. Items that grant "Slain Monsters Rest in Peace" such as the [ [Unique_Rings|Nature's Peace Unique Ring]], are also useful. Cold attacks can help by shattering the corpses, but the Ice Spawn that surround Nihlathak are immune to cold in Hell, so can not be shattered on that difficulty level.