M-Twins
The M-Twins (Nicole and Claudette St. Croix) are fictional comic book superheroine, mutants who appear in the X-Men family of books published by Marvel Comics. Created by writer Scott Lobdell and artist Chris Bachalo, she/they (as M) originally was a member of the teenage mutant group Generation X, and have not appeared in the series since Generation X #58. Lobdell, the creator of M and Penance, never intended for there to be a "real" M - only the twins.
Read more about M-Twins: Powers and Abilities