Part Two Kitty Pryde/Velocity/alwaysfaster: Quicksilver's powers Kitty's actually a lot like her canon counterpart. Just really fast. And she does have a little bit of an impatience issue like canon-Quicksilver. Mostly because everyone else is so. damn. slow. Overall, she's book smart, enjoys computers, books, and math, does gymnastics, etc. etc. She likes to welcome brand new arrivals because she knows she was freaked out when she first arrived to the school if only because it was a brand new, unknown place. She's been there since she was 12 (she's 15 now) so it's been a few years and she's settled in pretty well. Kitty has a good relationship with her family and doesn't have the tragic past that a lot of other people at the school have. So, in that respect, she's a bit naive to the game. Which might make her a little annoying.
Tabitha Smith/Phase/walkingthruyou: Shadowcat's powers Tabitha is... a pain in the ass. She's also a lot like her canon counterpart except now she can walk through walls which, while less destructive than time bombs, gives her a hell of a lot of opportunity to get into a lot of trouble. She's always testing limits, always playing pranks, a chatterbox, and really doesn't give a fig about authority. She does come from a troubled past, though it's not something she talks about. Telepaths/empaths/precogs might know something about it (and they're all welcome to know that her parents were divorced, she had a stepmother, her father was an alcoholic and abusive, etc. as you wish... no need to hold back your characters' powers there).
Mostly, she hides the pain of her childhood with her bombastic personality. She actually likes getting into trouble. And is probably always trying to plan an unwelcome party that includes underage drinking.
Laurie Collins/Ambrosia/laurieheals: Elixir's powers Laurie is a bit more outgoing than her canon self. Without the need to withdraw into herself due to her powers, she had a chance to be more friendly and wasn't so worried about "forcing" people to like her. However, she takes her healing powers very seriously. As a result, she ended up driving herself to exhaustion over and over and Jean stepped in, messed with her DNA, and screwed up, severely limiting Laurie's ability to heal people. I pretty much did this so there wasn't a character running around who could heal everything making it impossible for characters to have colds, broken limbs, etc. without it feeling like a huge plot hole. But also so that she's available to save people from huge injuries/illnesses as needed and/or wanted.
She spends a lot of time in the medical lab and has started to focus on learning about medicine since she can't just touch and heal as easily now. Though that makes her extremely frustrated and more than a little cranky.
Alison Blaire/Voodoo/ghostbitch: Wicked's powers She's a famous music star, all over TMZ, with a rep for being a total biyatch. Though she tells the press that it's all just people making up stories. They tried to make her go to rehab and she said no, no, no. And stuff.
She arrived at the school this past April. Before that, no one knew she was a mutant but she had an on stage incident (it's ghost time baby) that outted her and ended up being a scandal. Which basically ruined her career. She was sekritly sent to Xavier's where she has to spend most of her time incognito since no one knows that Xavier's is a mutant school. It's making her crazy.
Selene Gallio/Styx/blackhellfire: Magik's powers Part of the Hellfire Club, history teacher, came to the school after Emma did to figure out what was up with her blonde frenemy. The HFC seems to be gathering at the school, so they've got their own little club within their club. They should have Fight Club.
She's very pro-mutant superiority. Owns a bunch of nightclubs around the world, including one in Manhattan that's an underground mutant only club. And is rich as fuck. She's was also born forever ago and has time traveled via her powers in skips and leaps (along with a little sorcery help) to end up in the present.