Spongebob, Friend of All

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.