Cetus

Echo
Cetus may not attack an opponent who controls no blue mana-producing lands.
If you do not control an island at the beginning of your turn, sacrifice Cetus.
Monstrosity 3: {u}{u}{u}
When Cetus becomes monstrous, detain up to three creatures.
...the Nereids were angry, and Poseidon, sharing their wrath, sent a flood and a monster to invade the land. -Apollodorus