1) Slipstream
Slipstream‘s power sounds appropriately weird and mutant-y when you read the official description: he can “generate a warp portal in the fabric of space and ride the resultant warp-wave… Slipstream could use this ability to travel to virtually any point on Earth at faster-than-light speed, and can ferry others through the portal with him.” Unfortunately, this translates to “surfboard-based teleportation,” which is less useful and not at all cool. Slipstream can teleport, but only when he’s on his little surfboard and making an appropriate surfing-like pose, meaning he has to carry along an official X-Men boogie board with him wherever he goes if we wants to catch those waves, dude. It’s ridiculous that the Silver Surfer hasn’t beaten him to death.
3) Stacy X
Here’s a clue for all aspiring X-Men out there. Does your code name have an X in it? Then you are trying way too hard. An X-Man has an X in his or her name is certain to be trying to be cool, and Stacy X, whose hilariously “extreme” upbringing included her being part of a mutant brothel. This was actually fortuitous, since her mutant power was using pheromones to make people have orgasms (or vomit, or other things) — well, that and having snake-skin. Stacy X is clearly someone’s attempt to make the X-Men seem more adult and edgy by including a character who once had sex for money. Doubt me? Here’s what she did upon leaving the X-Mansion: “She left behind for [Archangel] a video of herself jumping rope naked, stating that she didn't want to stay around them and taunting him that he missed the chance to have had someone as sexy as herself as a girlfriend.”
6) Jubilee
Jubilee’s mutant power is to shoot fireworks. These can be used as offensive weapons, in the same way regular fireworks can be used as offensive weapons, and that if you light one and throw it at somebody and it hits them it’ll hurt. But when your team is full of dudes with metal claws, guys who can fire concussive blasts from their eyes, or control people’s minds, the girl who’s effectively carrying a bunch of bottle rockets around with her isn’t going to be of much use. That’s probably why Jubilee has gone through more uniform and codename changes than Jean Grey has had resurrections, because 20 years later still nobody has figured out what to do with her.
7) Ink
There have been a few characters in pop culture who have super-powered tattoos; it should be no surprise that the X-Men have one, too. But Ink is unique among these characters in that 1) he has no powers, because there’s another mutant named Leon whose powers is giving power-bestowing tattoos and Ink is just a moron; 2) Ink has, literally, seven tattoos, when he could be covered in them and become the most power dude on the planet; and 3) his tattoos are really fucking ridiculous. A caduceus on his hand lets him heal people, while a tattoo that vaguely resembles Colossus’ metal skin gives him super-strength, which is complete nonsense. If the tattoo designs can be that vague, then he could get the same powers with tribal armbands, a tramp stamp or a Tasmanian Devil. For the record, I have no idea why he's punching that maid.
11) Beak
Beak has a beak. He also has feathers. He is a birdman, which could theoretically be useful except he cannot fly. He can glide a little, and he wore a suit that allowed him to fly, but without the suit he is literally just a dude with a break. So really, if the X-Men had some kind of situation where they needed corn pecked off the floor quickly, Beak would have been vaguely useful.. until you remember the telekinetics who could grab the corn with their minds, or Storm, who could blow the corn away, one of any other thousands of mutants with the ability to move corn kernels more quickly than Beak could peck them.
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List is missing Maggot and Wraith