Blood Clock

Oracle Text

At the beginning of each player's upkeep, that player returns a permanent they control to its owner's hand unless they pay 2 life.

Card Rulings

6/1/2005 A player who controls no permanents doesn’t need to pay 2 life (although that player can choose to do so).
6/1/2005 A player with less than 2 life can’t pay 2 life and must return a permanent.
6/1/2005 The choice of which permanent to return or whether to pay life is made as the triggered ability resolves.