It Knows You

Flying, Indestructable
It Knows You is not a creature unless there is 40
or more cards among all graveyards.
Whenever a card enters your graveyard from your library, each opponent mills 1.
If that card is put there by the effect of surveil,
each opponent exiles the top card of their library
face down. You may look at cards and cast exiled
this way, as long as they remain exiled.
You may use any mana to do so.