Mutant Shark

The Mutant Shark, also known as the Hunter of the Seas, is a magical creature introduced in Season 8. The Mutant Shark was originally a normal shark from the ocean depths of Andros until Valtor used a dark spell on the shark to mutate it into a dangerous creature.

Appearance
Prior to its mutation, the shark was a gray-colored hammerhead shark. After its mutation, the Mutant Shark's dorsal fins were transformed into a row of sharp back spines running from the top of its back to the beginning of its tail fin, which became much longer. Its pectoral and pelvic fins were transformed into forelimbs and hind limbs ending in clawed and webbed fingers, and it gained an additional pair of eyes.

Season 8
The Mutant Shark was created by Valtor to keep the Winx occupied while Obscurum and the Staryummies attacked the core of Gorgol. It then ambushed the Winx and engaged in a lengthy battle against them. After realizing that their Sirenix magic cannot cause direct damage to the monster, Aisha suggests that the Winx would have to destroy Valtor's dark magic to make the Shark normal again. As for now, the Winx contained the Mutant Shark inside a cave. It is assumed that the Mutant Shark reverted back to its normal form after the Winx destroyed Valtor's dark magic.

Magical Abilities
Being a creature of darkness, the Mutant Shark is impervious to Sirenix magic. It has enhanced strength, as seen during its first battle against the Winx where it is able to break free from the seaweed conjured by Flora. In addition, it is able to shoot red energy beams from its tail fin.

Trivia

 * The mutant shark's appearance is similar to that of Slattern from the Pacific Rim franchise. However the mutated shark has only one shark-like tail instead of multiple tentacle tails like Slattern.