Lurking Spinecrawler

When Lurking Spinecrawler enters, you may choose a nonland card in your hand. If you do, that card perpetually incorporates {1}{B} and gains "When you cast this spell, each opponent sacrifices a creature. Each opponent who can't discards a card."
Whenever you cast a multicolored spell, for each of that spell's colors, each opponent loses 1 life and you gain 1 life.