RiddleTimer Sphinx

Flying
Vanishing 4 (This permanent comes into play with
four time counters on it. At the beginning of your
upkeep, remove a time counter on it. When the last is removed, sacrifice it.)
When RiddleTimer Sphinx enters the battlefield,
tap target creature. It doesn't untap during its controller's untap steps. When RiddleTimer
Sphinx leaves play, untap that creature.