Prometheus Black

Proxy: Jodah, The Unifier
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.