She is a member of the flagship team of X-Men in her reality, Earth-9997 (Earth-X). Though she can fly through and breathe air, she is also able to breathe and swim through water. She is an ichthysanthrope (Were-Fish) or a fish/human hybrid.

Mermaid

She is a member of the flagship team of X-Men in her reality, Earth-9997 (Earth-X). Though she can fly through and breathe air, she is also able to breathe and swim through water. She is an ichthysanthrope (Were-Fish) or a fish/human hybrid.

All data from the awesome folks at Marvel.