Call for Blood 
Instant — Arcane
As an additional cost to cast this spell, sacrifice a creature. Target creature gets -X/-X until end of turn, where X is the sacrificed creature's power.
Legality
standardNOT LEGALpioneerNOT LEGALmodernLEGALlegacyLEGALvintageLEGALcommanderLEGAL