Anowon, the Ruin Sage
Worldwake — rare
Legendary Creature — Vampire Shaman
Anowon, the Ruin Sage rulings:
2010-03-01: When the triggered ability resolves, first you choose which creature you'll sacrifice (if you control any non-Vampire creatures), then each other player in turn order does the same, then all chosen creatures are sacrificed at the same time.
2010-03-01: If a player controls no creatures, or if all creatures a player controls are Vampires, that player simply doesn't sacrifice anything.