In the fictional Marvel Universe, secondary mutation is a global phenomenon among mutants that seems inexplicable, with many previously established mutant characters suddenly developing new or vastly expanded powers. Henry McCoyhypothesizes that, since the mutant population was entering the millions at that time, mutant physiology was responding to the need for survival. Thus in rare occasions a mutant's powers change or become even greater, and in rare cases they can develop a new, often unrelated ability. However, the criteria for secondary mutation is ill-defined at best, leaving many fans confused as to their favorite character's status or powers. This use of secondary mutations can sometimes be misused as a deus ex machina plot device; if the writer can't think of a way for a character to get out of a situation, they can simply develop a spontaneous new power to handle the problem.
Gambit (Remy Lebeau): Gambit is able to psionically suggest things to people using his hypnotic charm. It allows him to exert a subtle influence over sentient beings, leading them to believe what he says and agree with his suggestions. This charm is so powerful that if given a chance, Gambit could charm the Shadow King. However, the charm does not work on those who know about it. It is also a passive mutation and he cannot actively control it. He is unable to go up to a stranger and say "Jump off a bridge" but if the setting is right and he works up to it (in his trademark style) then he can influence people. He also has empathy and can feel—and according to some sources, influence—others' emotions. Gambit was recently blinded as one of his own kinetically-charged cards blew up in his face. During his state of blindness, he developed a precognitive ability.[volume & issue needed] When his vision was restored, this power disappeared.[volume & issue needed]
Polaris (Lorna Dane): after having her mutant powers leeched by her supposed-sister, Zaladane, Lorna developed the first recorded case. Her body mass had increased, along with her strength and resistance to injury. When her secondary powers were used, it developed negative emotions in anyone around her.[volume & issue needed] Later, Lorna regained her original powers after Zaladane's death, and her secondary mutation vanished.[volume & issue needed] This was retconned to be the first known secondary mutation when the concept was first introduced.[volume & issue needed]
Beast (Hank McCoy): He developed a higher level of power mutation after being seriously injured by the villain Vargas. Sage attempted to use her ability to "jump start" mutation to save his life. This resulted in Beast evolving from his original simian form into a giant feline form. However, it is unclear if this is a true secondary mutation or if this is the result of permanent alteration to his genetic structure resulting from self-experimentation and the mutagenic abilities of Infectia.[volume & issue needed]
Angel (Warren Worthington III): discovered his new power while being wounded in a battle with a group of werewolf-like mutants called the Dominant Species. Both he and his teammate Husk were severely wounded. Husk almost died, but was brought back through contact with Warren's blood seeping in through wounds on her own body. His blood gained a healing property that can be used to mend and regenerate others of the same blood type[volume & issue needed]. This activation was then retconned as having occurred earlier, in a battle against Black Tom Cassidy, when his skin turned from blue to normal (later described as a result of his healing factor activating)[volume & issue needed]. Angel had previously been modified by Apocalypse;[volume & issue needed] whether this included genetic alterations has never been clarified.
Iceman (Bobby Drake): his supposed secondary mutation was greatly increasing his ice manipulation abilities, but leaving him trapped in his organic ice form and unable to transform back to flesh and blood[volume & issue needed]. Many years ago, Emma Frost had previously shown Bobby a glimpse of these powers as he was able to live on as moisture.[volume & issue needed] However, after the events of M-Day, where over 90% of the world's mutant population became depowered, Bobby is once more able to revert and forth[volume & issue needed].
Black Tom (Black Tom Cassidy): Black Tom's original mutation allowed him to look like a normal human being with an ability to channel concussive blasts from wood. However, in Chuck Austen's Dominant Species storyline, Black Tom suffered a secondary mutation that left him as a half-plant creature with a lost sense of humanity.[volume & issue needed]
Phoenix (Jean Grey-Summers): After the storyline The Twelve, Jean Grey somehow managed to transfer her telekinetic powers to Psylocke, who also managed to transfer her telepathy to Jean Grey.[volume & issue needed] For a time, Jean only had telepathic powers[volume & issue needed]. However, when the NEW X-MEN series started, Jean's telekinetic powers had returned[volume & issue needed]. Beast implied that it was the result of a secondary mutation for Jean.[volume & issue needed] However, this appears to be retconned later, as it is revealed that at some unspecific point, Jean merged again with the Phoenix Force and that perhaps the Phoenix had given her back her telekinesis.[volume & issue needed]
Toad (Mortimer Toynbee): Toad's original powers have increased and he has gained additional powers through further mutation, including adhesive saliva, and a prehensile, elongated, protractible and sticky tongue. He also has gained the ability to extend his tongue great distances and ensnare objects and people. His tongue is superhumanly strong and tough to the extent that he once squeezed a magistrate of Genosha to death. He is also able to secrete an adhesive resin from his hands and feet that paralyzes the nervous system of any living organism that touches it. His tongue secretes odorless pheremonous venom that he is able to use to control minds to a limited extent. Toad also possessed the ability to psionically communicate with amphibian life (which he often uses as spies), and to expel powerful gusts of wind from his lungs capable of knocking someone down.
Havok (Alex Summers): During the Mutant X storyline, Alex is revealed to have the secondary mutation of being a Nexus point between himself and all other Alex incarnations across the omniverse. After dying in Earth 616, he wakes up in another alternate reality where he is the leader of a darker version of the X-Men team, and is later able to return to 616 using the Nexus of All Realities.
Although never fully stated as a secondary mutation, some other mutants had shown abilities that were very different from their primary mutation.
Elixir (Josh Foley): Initially, when Josh's healing powers manifest, he looked like a normal teenage boy[volume & issue needed]. However, after being brutally attacked by Wolfsbane, Elixir was forced to heal himself. The result of which, caused Josh's body to undergo a second, this time physical, mutation, turning his skin from flesh tone to gold.[volume & issue needed] Later, Josh's powers undergo another change, with the revelation of his death touch, which also turns his skin black.[volume & issue needed] Though this can be seen as the two facets of the same power to control human biological functions (both healing and killing) as opposed to just a healing power[original research?].
Wolverine (James Howlett): When Wolverine lost his adamantium skeleton, his body reverted to a more feral state, looking completely different from his human form.[volume & issue needed] Whether this was a secondary mutation remains to be shown, although it could have been his body regressing as opposed to a mutation of sorts[original research?]. It has been later shown that unlike other mutants, Wolverine constantly mutates, but this process is typically retarded by the adamantium in his skeleton forcing his body to expend most of its effort on preventing him from dying of metal poisoning.
Siryn (Theresa Cassidy): Siryn's secondary mutation first appeared in the new X-Factor series. Siryn is able to influence and control other human beings with her psionics, as well as cause them to enter a hypnotic state. Siryn can also cause the intended person to fall in love with her without regard to gender or sexual orientation and carry out her wishes and commands, like mythical Sirens. Siryn once utilized this ability on Spider-Man, forcing him to divulge the truth about the Decimation of the mutants. It hasn't been clarified as to if she has developed a secondary mutation or has further developed her abilities.
Sharon Ginsberg: Sharon's original power was her large bat-like wings that extended from the upper part of her back and were capable of allowing her flight. When they were removed, and Sharon awoke in a hospital, she manifested tough, sharp claws instead of finger nails and tough, sharp fangs instead of teeth, and advanced strength and speed levels. She was able to quickly flex and snap out of the restraints she was in at the hospital, and her claws were sharp enough to kill Solomon O'Sullivan. It is unknown though if this was a new mutation or simply part of her original bat-like mutation, to go along with her bat-like wings.