David, Crafter of Lore

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.