Skulltrap, 3rd level wizard spell (Necromancy, Evocation): "This ward may be placed on any non-living skull or the skull of an undead skeleton." It remains dormant until touched by living matter or struck and damaged by a weapon, then it explodes with a flash of red or violet light in a 10 foot radius. (Karl Waller, AD&D 2e Dungeon Master Guide Rules Supplement The Complete Book of Necromancers by Steve Kurtz, TSR, 1995)
I love any variation on the ordinary humble animated skeleton. One or more skeletons bearing skulltraps could be a surprisingly difficult encounter.
















