9. Nightcrawler Turns On The X-Men - Ultimate X-Men Annual #2 (2006)
When Marvel rebooted under the Ultimate Marvel banner, many characters were heavily revised. In this version, Kurt Wagner AKA Nightcrawler, was a victim of the Weapon X program. Weapon X tortured Kurt for years, leaving him rattled and unstable.
When the X-Men rescue Kurt from the facility and give him a new lease on life, they didn't realise how deeply Weapon X had taken a toll on his mind.
When Kurt develops feelings for fellow X-Man, Dazzler, he becomes obsessive and begins stalking her. When he finds out his teammate, Colossus, is gay, Kurt is so disgusted, he abandons the team. He then tells Dazzler that the X-Men are dead and teleports her to a cave where he hopes to look after her.
When the X-Men learn that Kurt has had a nervous breakdown, Wolverine tries to talk to him, but he flies into a rage and becomes violent. When he admits he fantasises about Dazzler having his children, only then do the X-Men realise their friend has truly lost it.
Professor X does what he can to heal Kurt's fractured mind, but things were permanently tense between Kurt and Dazzler for the rest of their time on the team.