Xlyym was a mutant Fomalhauti working with Skeletron who was dispatched to Earth's Atlantic Ocean to create a diversion. He brought with him his personal Banari (who had been turned into a servitor race via his Skullhuggers) and was going to use two Earth-Movers to shift the Earth's axis therefore melting the polar caps and flooding the continents, in the process getting a new homeworld for the Fomalhuati.
Namor and his allies (Triton, Tiger Shark, and the Banari Tamara Rahn put an end to that plan, during which Xlyym's Banari consort Trieste Rahn died. Afterwards he attempted to create a tidal wave as a new distraction and was prevented in doing so by the Fantastic Four who used the Stealth-Hawk to attack his ship. He was rescued from the sinking vessel and then slain by Tamara Rahn to avenge what had happened to her fellow Banari.
as other Fomalhauti, Xlyym communicates telepathically and manipulates objects by forming tentacles.