Neptuna

Neptuna is the first boss on Desert Island, in The Deadly Tank of Neptuna. He was created by Baron Dante's magic that made a fish (a tuna, presumably) into a trident-wielding demon. He probably got his name from being turned from a fish and holding a trident, and just acting like the old Roman God of the sea Neptune. He is one of the hardest bosses to beat, and being underwater the whole time doesn't help.

It's Neptuna!