Depth lurker

Islandwalk, double strike, drag down (when you block a creature, destroy it)
{u/b}{4}{t}-Seaspawn- create a token that is a copy of this creature
{b}{u}{4}-Lash out{dash}Pay 5 life, destroy all creatures that aren't depth lurker or a depth lurker copy token
Depth lurker can't be blocked or deal damage to creatures without blue in any of their mana costs