Lazav, Echo of the Losts

Delve
When you cast Lazav, each player exiles the top
X cards of their library. You may have Lazav
enter the battlefield as a copy of any creature
card exiled this way with mana value X or less,
except its name is still Lazav, it's stil legendary
and it gains "{u/b}{u/b}: You may cast a noncreature
card from exile with mana value lesser than
Lazav's power without paying its mana cost.
Return Lazav to its owner's hand"