Dream Tides

Oracle Text

Creatures don't untap during their controllers' untap steps.

At the beginning of each player's upkeep, that player may choose any number of tapped nongreen creatures they control and pay 2 for each creature chosen this way. If the player does, untap those creatures.

Card Rulings

2/1/2006 You can only untap nongreen creatures once, since this has a beginning of upkeep triggered ability.