Polaris Queen Cassiopeia

Whenever a nontoken creature enters the
battlefield under your control, look at the top X
cards of target opponent's library, where X is
that creature's converted mana cost. Exile one of
those cards and put the rest back on top of that
player's library in any order.
I am the queen of the stars, Cassiopeia. I stand firm
in the middle of the sky, piercing through the darkness
of the universe.