Reprint and retroactive backup story to The X-Men #122 - Cry for the Children (June, 1979).
Who Am I?
Dressed in a devil costume, Nightcrawler arrives at a Halloween party where his true identity is known to the host and the other X-men, who've all arrived separately in disguises of their own. After being told by his host that his help as a hero is required, Nightcrawler helps himself to refreshments and tries to figure out which of the guests are his teammates.
After flirting with another guest, Nightcrawler is again joined by his host; he explains that one of the other guests, who's dressed as a ghost, had received a threatening call from her abusive ex-husband. She and the host both suspect that the ex-husband is at the party, but with everyone in costume, they don't know who or where he is.
Elsewhere at the party, Cyclops is dressed as a jester, and notices a veiled woman dressed as a belly-dancer is making eyes at him. He's taken aback noticing how suggestive he finds the woman based solely on her eyes, and thinks that Jean would never be so forward. As he returns longing looks with her, he feels guilty about it because of his relationship with Jean, but he still feels compelled to follow her when she beckons. Following her into a dark corner, the two of them both lean in for a kiss, but under the woman's veil is another mask, of the lower half of a woman's face. Asking if he can remove that mask, he finds a scarred mouth leering back at him, asking "what's the matter, lover-boy? I thought you liked me--"
Before Cyclops can respond, however, the woman is cut off by a loud scream from another room. Investigating, Nightcrawler sees a woman dressed as a ghost stabbed in the neck, and shuts the door saying that no one must leave the room. A man dressed as a clown rushes past him, only to be stopped by a mummy that turns out to be Colossus. Trying another exit, the clown is stopped by a nondescript pile of laundry that turns out to be Wolverine.
Cornered, the man grabs a woman dressed as a witch and holds a knife to her throat, threatening to kill her, but as he does he's interrupted by the woman dressed as a ghost, saying that he hadn't really killed her and that he'd only killed a dummy. Distracted, the man loses his grip on his knife as it's telekineticly lifted away from him by the woman dressed as a belly-dancer.
Now realizing that the belly-dancer was Jean all along, Cyclops rushes over to apologize. Jean just makes fun of him for not recognizing his own girlfriend with gross makeup, and then they make out.