The Tarnished, Elden Lord

Legendary creatures you control get +X/+X, where
X is the number of legendary creatures you control.

Whenever you cast a legendary spell from your hand,
exile cards from the top of your library until you
exile a legendary nonland card with lesser mana value.
You may cast that card without paying its mana cost.
Put the rest on the bottom of your library in a
random order.