Anowon, the Ruin Sage

Oracle Text

At the beginning of your upkeep, each player sacrifices a non-Vampire creature.

Card Rulings

3/1/2010 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.
3/1/2010 If a player controls no creatures, or if all creatures a player controls are Vampires, that player simply doesn’t sacrifice anything.