Banshee

Sean Cassidy was a young rich mutant with undiscovered powers. His parents died, leaving him and his cousin Black Tom Cassidy with a huge fortune and the castle they had grown up in, called Cassidy Keep, although as Sean was the rightful heir, he gained all of it. The castle was a strange place, where leprechauns lived under the protection of the Cassidy Family. Both Sean and Black Tom were mutants; Sean's power was a sonic scream.

Factor Three, a villain team, discovers him and their leader, Changeling invites him to join. Sean is horrified and refuses, but Factor Three trick him and set explosives next to his head. He is forced to do their bidding, or they would detonate the explosives. After working for them for a long time, Sean runs into the X-Men on a mission in New York. Professor X easily disarms the bombs and Sean, codenamed Banshee, helps the X-Men stop Factor Three. Banshee is kidnapped by the Sentinels a few months later, and the X-Men save him again. Professor X asks him to join the X-Men when the original team is captured by the living island known as Krakoa, who wanted to feast on them. Banshee, Sunfire, Nightcrawler, Colossus, Storm, Thunderbird, and Wolverine all manage to stop Krakoa and save the original X-Men. These seven (minus Sunfire, who quits) form a new team of X-Men after the original team leaves (with the exception of Cyclops, who stays on as team leader). Banshee is reluctant at first, as he was much older than the rest of the X-Men, but Professor X manages to convince him to stay.

X-Gene Mutation: Banshee is a mutant whose superhumanly powerful lungs, throat, and vocal cords could produce a sonic scream for various effects, in concert with limited, reflexive psionic powers which directed his sonic vibrations. He could generate sonic blasts which struck with tremendous concussive force, liquefying or outright disintegrating targets at his highest levels of power.

Flight: He could hover or fly at the speed of sound, and could carry at least one passenger. Targeted Attacks: He could overwhelm listeners with deafening noise, stun them with tight-focus low-frequency sonic blasts, plunge them into a hypnotic trance, disorient them, nauseate them, or simply render them unconscious. Frequency Manipulation: Using sonic waves, he could rapidly vibrate himself or other masses at will. By radiating sound waves outward and reading the feedback, he could locate and analyze unseen objects in a sonar-like fashion. By modulating his scream's harmonics, he could confuse most scanning equipment. He could instinctively analyze, replicate, and block sonic waves or vibrations from other sources. Immunity: Banshee generated a psionic field which protected him from the detrimental effects of his sonic vibrations, though his sonic powers could still injure him when pushed beyond safe limits. His physiology seemed fully vulnerable to conventional injury when his sonic powers were not engaged.

Attention: Banshee had selective hearing, enabling him to focus upon, enhance, or totally block out any given sound in his environment; this shielded him from the deafening sound of his own screams, and made him a superhumanly acute eavesdropper in surveillance situations. Lineage Limit: Banshee and his cousin, Black Tom Cassidy, were unable to effect each other with their powers as a result of their family heritage.