Desecration Elemental

Oracle Text

Fear (This creature can't be blocked except by artifact creatures and/or black creatures.)

Whenever a player casts a spell, sacrifice a creature.

Card Rulings

12/1/2004 This ability triggers off anyone casting a spell, including you, not just Desecration Elemental’s controller or an opponent.
12/1/2004 If Desecration Elemental is the only creature you control when its triggered ability resolves, you’ll have to sacrifice it.