Call for Blood | Magic: The Gathering
Formats Call for Blood is Legal in
Official Oracle Text for Call for Blood
Target creature gets -X/-X until end of turn, where X is the sacrificed creature's power.
Official Rulings for Call for Blood
2/1/2005 : You may sacrifice the creature chosen as the target for Call for Blood (if you control it) when you pay the additional cost for the spell. If you do, Call for Blood is countered on resolution.
4/15/2013 : You must sacrifice exactly one creature to cast this spell; you cannot cast it without sacrificing a creature, and you cannot sacrifice additional creatures.
4/15/2013 : Players can only respond once this spell has been cast and all its costs have been paid. No one can try to destroy the creature you sacrificed to prevent you from casting this spell.