Sea dragon leviathan

Ah yes this thing is 160meters in size and can fire fireballs from its mouth and bite plus use its claws

Fun fact: The model for the Sea Dragon Leviathan was the original concept for the Sea Emperor. It was replaced by the current one because the menacing appearance of the model, with its menacing claws, touch scales, and sharp teeth, didn't fit with the Sea Emperor's naturally peaceful demeanor.

Good to know, but in fact, the sea dragon is the only leviathan that can one-shot you

Fair point. Though, in theory, if the Sea Emperor was real, the mere fact of it using telepathic communication could probably kill you since your mind wouldn't be able to properly understand how that's happening. Either your brain would explode or it would shut down.