New Mutants/YMMV

YMMVs for the first series:

 * Alas, Poor Scrappy: When Cypher was killed off, people felt real bad.
 * Rescued From the Scrappy Heap: Since coming Back From the Dead.
 * Alien Scrappy: Warlock and Gossamyr; Shatterstar also probably counts when written by Rob Liefeld
 * The presence of extraterrestrials on a mutant team was handwaved away since they had different personalities than those typical of their species (this was lampshaded and parodied in an issue of What The...? where the New Mutants parody team had a stray dog join for similar reasons).
 * Warlock actually was a mutant of his species, however, as unlike the rest of the technarchy, he was able to infect people without it being permanent, and absorb life energy without killing them.
 * Complete Monster: Two in the forms of Empath and Donald Pierce.
 * A bio by Xavier flat-out states that Manuel may be the definition of pure evil. In addition, he has no empathy and toys with others' emotions for his enjoyment.
 * Pierce is not only a racist mutant hating cyborg, but he also goes after the babies and children first because he's too scared of what the adults might do to him.
 * And he thinks that going after the kids wouldn't spark a reaction? An angry, violent reaction considering what Emma Frost and Wolverine are capable of?
 * Crowning Moment of Awesome: The Devil Bear Saga, for both Dannielle Moonstar and the creative team themselves.
 * The Magus is probably among the most powerful foes any X-team has ever faced, and the New Mutants squad, the Professor, and a cosmically-powered Carol Danvers ended up stopping him. And Doug Ramsey was the guy who won the battle.
 * Crowning Moment of Funny: In new series Dani gets her friend - congnitive therapist - to try to work around personal issues of her teammates and Nate Grey. She has to explain to him Summers Family Tree.
 * Crowning Moment of Heartwarming: Nate Grey is getting those in new series, first with Cyclops assuring him he is finally home and second with Hope Summers taking him under her wings, despite all issues she must have with his pressence.
 * Does This Remind You of Anything? : Doug and Warlock fusions could be sexual metaphors.
 * Ensemble Darkhorse: Rahne has been a member of more X-Men spinoff teams than any other character.
 * Hey! How'd you chumps go so long without adding yours truly to the page, huh?! HUH?!
 * Fetish Fuel : Selene and her mind control could be used quite erotically; when she forces Mirage to enjoy the sacrifices, for example.
 * High Octane Nightmare Fuel: The Demon Bear Saga
 * Empath's powers and the way he uses them. He has absolutely no qualms about manipulating another person's emotions against their will all because he thinks it's amusing.
 * The Smiley Faces.
 * Les Yay : The link between Rahne and Dani.
 * Moral Event Horizon: Pierce crosses this several times in the New Mutants origin story alone. Examples are ordering the death of Dani's grandfather and having his men trying to kill each of the New Mutants who were, at the time, teenagers who had only just discovered their powers.
 * The Ani-Mator also crossed this by killing Cypher.
 * The Scrappy: Where to start? Warlock. Gossamyr. Cable.
 * Bird Boy is probably the most extreme, being an imbecilic half-animal who derailed the book into whacky antics and over-eating. He's actually one of the most-accurate in-continuity versions of the Jackovasaurs from South Park. At least he was rapidly Put on a Bus.
 * An entire team of Scrappies was folded in following the Inferno event with the X-Terminators: Boom Boom, Rusty, Skids, Arty, Leech, Rictor, Whiz Kid. Luckily the bulk of the characters were quickly put on various buses, leaving Rictor and Boom Boom to become beloved members of the group, though this derailed the book from a thoughtful angsty series into the very "mall-going brats" adventures that old-school fans thanked the old writers for not using.
 * Cypher too, but his death was an Alas, Poor Scrappy moment and since his return, he's been Rescued From the Scrappy Heap
 * They Changed It, Now It Sucks: The level of "dumbing down" from the earliest issues to the time of Cable's leadership is so marked that it also marks the beginning of the Liefeld Age of comics; chrome arms, pouches, guns, pointless angst, no-character writing, teeth-gritted action, "ninjas appear from the future", etc.
 * They Wasted a Perfectly Good Plot: Cypher was a polarizing character amongst fans of the title in the 1980s, in part because he had sensible everyday mutant powers in the form of the ability to understand any form of language, which sadly also made him utterly useless in fight scenes unless he merged with the alien Warlock. So when Chris Claremont left the book and Louis Simonson took over, Simonson decided to kill off Cypher since she didn't feel like coming up with excuses for why he was MIA in fight scenes, plus felt that no one liked him. Sadly, when she killed him off, fans revolted against the death. Even the fans who were calling for Doug to be killed off! And to this day still fans rant and rave about how Cypher had so much potential that was utterly wasted by Simonson misreading the room.
 * It's a real shame that Doug was killed before the internet became near-universal or he could have been the world's greatest hacker.
 * Cable versus Apocalypse/The Twelve, which was the replacement for the Highlord Ascension storyline when it was dropped, was haphazardly aborted for a lame-ass month-long event called "Ages of Apocalypse" involving the X-Men in different time periods play-acting various scenarios.
 * Tear Jerker: The issue that dealt with Ilyana's death - or, rather, Jubilee's reaction to it. Even the knowledge of Comic Book Death and the likelihood of Ilyana's eventual return wasn't enough to dampen the emotional weight of a tale about a little girl slowly dying as the adults around her slowly come to the realization that there's nothing they can do to help. Although "I won't allow her to be placed into a living death!" isn't a good argument when it might have allowed them time to find a healer and it certainly would have allowed time for her brother to get home before she died.
 * Unfortunate Implications: Magma falling for Empath after repeatedly being mindraped by him.
 * Danielle Moonstar who is a walking Native American stereotype at times, right down to her mistrust of "whites". Which is amazing given the team also includes a hulking Apache warrior.
 * The Woobie: Rahne. A couple of her old teammates have had worse backstories, but few radiate please hug me as much as she when they are down over it.

YMMVs for the second series/New X-Men:

 * Complete Monster:
 * William Stryker, of course. Kyle and Yost evidently disagreed with Chris Claremont that he could be redeemed, as they explicitly undid Claremont's redemption storyline for him.
 * Possibly also Sean Garrison, had his arc not been aborted. He is a mind rapist and actual rapist, after all.
 * Internet Backdraft: Whoo boy, DeFilippis/Weir vs. Kyle/Yost. DeFilippis has been known to defend Kyle and Yost from angry fans, for what it's worth.
 * The Scrappy: Icarus. You'd think this would be because of acting like a moron and inadvertently getting himself and half his friends killed in the first Kyle/Yost arc... except nobody much liked him under DeFilippis and Weir, either.
 * Thirty-Sue Pileup: X-23 under Kyle and Yost, no ifs, ands, or buts about it. Fittingly, they created her.
 * Copy Cat Sue: Duh!
 * God Mode Sue: Seems to gain a new animalistic sense whenever the plot calls for it, enabling her to figure plot points out before anyone else.
 * Jerk Sue: Has the personality of a coldhearted assassin amongst largely naive, inexperienced teenagers.
 * Relationship Sue: Gets involved with Hellion after Wind Dancer is shooed out of the plot off-panel.
 * Sympathetic Sue: A candidate for the most messed-up backstory of any X-character.