Ertai's Familiar

Phasing (This phases in/out before you untap during each of your untap steps. While it's phased out, it's treated as though it doesn't exist.)

When Ertai's Familiar phases out/leaves the battlefield, put the top three cards of your library into your graveyard.

[U]: Until your next upkeep, Ertai's Familiar can't phase out.