Sands of Time

Enchant creature
When Sands of Time enters the battlefield, tap enchanted creature, and then put X sand counters on it. As long as enchanted creature has
a sand counter on it, it doesn't untap during it's controller's untap step.
Remove a sand counter from enchanted creature at the beginning of its controller's upkeep. Then, if it has no sand counters on it,
detach Sands of Time and put it on the bottom
of its owner's library.