Mother Tideswell

As you play a basic land, you may choose a Kraken, Leviathan, Octopus, or Serpent you control and pay its mana cost. If you do, that land enters the battlefield as a copy of it.
"Now, I'm sure that your navy was the big fish in whatever small pond it came from. But the sea is no small pond. And the fish are the least of your worries."