Supporting the theory that Vanessa (with a mermaid tail) was her original form, she dabbled into dark magic to increase her powers, jealous as she was of her brother Triton and all the recognition that he got. To assume immortality she created horcruxes, which eventually distorted her body until she sprouted a few more tails and became the fat octopus we see today. It makes sense in every way; she hid in the Leviathan corpse because nearly all of her horcruxes had already been destroyed (hence her line "And now, look at me - wasted away to practically nothing"; she was referring to her lack of Horcruxes). It also explains why she was so horrified when her eels died (guess why their eyes were so vibrant? They were Ursula's personal Naginis!) and that she died only after the eels, her final