Anivia, the Cryophoenix

Flying
Freeze (Whenever this creature blocks or
becomes blocked the other creature does not untap
during its owners next untap step.)
When Anivia dies, create a 0/1 white blue
Elemental creature token with "At the beginning
of your upkeep, sacrifice this creature and return target card named Anivia, the Cryophoenix from
your graveyard to the battlefield."