Mutant deep sea leech testicles.
It actually belongs to the same family as certain octopuses and shellfish.
Could make a good terraria boss.
What I was thinking as well. It is able to shoot a giant laser, many, many bullets, and missiles. It repeatedly slaps with its tentacles and spawns up to four smaller parts that can shoots small lasers and ram. It would blow up when it is defeated.
Then again, fighting a boss in the ocean is hard, considering one has to have the mermen pendant or gills potion. It could possibly spawn in a trench, if the ocean is ever extended to reveal glaciers, sunken ships, big coral reefs/seaweed forests.
