Creature — Avatar 4/4, 3WW (5)
Rare
At the beginning of your upkeep, you may choose a card type. If you do, each player sacrifices a permanent of that type.
"Why fight the world when you know who will win?"
—Nissa Revane
Illus. James Paick

10/1/2009: You may choose any card type, including instant or sorcery. Choosing instant or sorcery will result in no permanents being sacrificed, though, since no permanents have those card types.
10/1/2009: You don't choose a card type until the ability resolves. Once you choose a type, it's too late for players to respond.
10/1/2009: First you choose which permanent you'll sacrifice (if you control any of the chosen type), then each other player in turn order does the same, then all chosen permanents are sacrificed at the same time.
Legal in Vintage (Type 1)
Legal in Legacy (Type 1.5)
Legal in Extended (Type 1.X)
Legal in Classic (MTGO)
Legal in Commander
Legal in Modern