Angel cautiously walked through the Sunnydale night, doing his best to avoid falling flat on his face at every step. His careful gait was due to not only his new footwear of large, clunky brown shoes, but also a certain piece of apparel that the vampire had never previously worn before in his entire, centuries-long existence. Either as a living human, or an undead creature of the night. Struggling to ignore how his novel clothing shifted around his body, both rubbing against unexpected places and leaving exposed to the cool night air other formerly protected areas, Angel tried to distract himself with a mental pep talk that this wasn't so bad, even if he had to search through the quiet city streets for Buffy.
After Xander left, Angel had dithered throughout most of the day about whether to wear the costume or not, particularly when he'd lifted it off the table in order to examine it more closely, and discovered the rest of it, including the necessary makeup. Oddly enough, this last item had finally persuaded Angel to go along with the whole absurd proposal, since using this meant that nobody would recognize him at all. Once he'd slathered all of the greasepaint on his features and other exposed flesh, and then added the other theatrical cosmetics, plus the required accouterments and finally the costume itself, Angel had incredulously stared down at his form in his newest attire, which fit perfectly. After checking everything against the colorful picture on the brochure guide that had come along with the outfit, for the first time in his entire demonic existence, the vampire had then been truly thankful that he could no longer see his reflection in mirrors.
It'd taken the last of Angel's rapidly-vanishing stock of courage for him to venture out of the mansion, and he'd been about to bolt back into this building's sheltering cellar, when the very first encounter with other Halloween trick-or-treaters had taken place, right in front of his dwelling. As he'd stood there in paralyzed horror, the small group of kids in their own costumes escorted by parents outside in a rare, safe Sunnydale night had walked right by him on the sidewalk. The entire party had curiously eyed the tall man standing frozen in his absolutely accurate All-Hallows attire, and they'd then responded with…cheers and applause.
Well, even though the vampire had next heard from further down the block some of the younger children asking exactly who that had been, and after it'd been explained to them, nobody had anything bad to say about this, or even concerning him. Just admiring comments of how clever and funny it'd been to see someone dress up as that in so much detail. It'd all wound up with a remarkably relieved Angel, who in his ensuing travels through Sunnydale in his search for Buffy, had heard mostly the same thing about his evening wear from other costumed revelers on the streets.
As he passed through one of the town's mixed residential/commercial sections, Angel sniffed the air, and the vampire halted in his tracks at recognizing a truly familiar scent. Buffy had been around here just a few minutes ago! Let's see, the Slayer's scent was strongest in this direction-
At that very moment, a ceremony being held in the back room of Ethan's Costume Shop came to an end, with the concluding shouted word of "JANUS!"
In his mental prison deep inside the ensouled vampire's mind, a true monster immediately came awake, as his unknowing host at last experienced the exact conditions of the curse cast over a century ago by a Gypsy tribe furious over the murder of one of their own by the fiend calling himself Angelus. Taken over by the Chaos magic in his costume, Angel now underwent one moment of pure happiness.
Feeling his despised doppelganger vanish, Angelus burst into actual existence into the world once more, ravenous for blood and slaughter, inside a brain and body that was…that was…
Nobody at all - not Angel, Angelus, the Kalderash tribe, Whistler, the Powers That Be - had ever pondered the potential loophole in the curse that just now occurred right then and there in the Sunnydale street: 'One moment of pure happiness.'
What if it was a lot longer than that?
Desperately trying and failing to gain control over a mind already occupied by a joyful personality forever in a state of permanent bliss, which didn't even begin to notice something so different as Angelus currently sharing their consciousness, this evil creature began to writhe in his mental agony from being bathed in waves of pure, innocent delight that…just…wouldn't…STOP!
Finally, in a last frantic attempt to maintain his very survival, Angelus' suffering spirit hastily cast himself out of the euphoric psyche at that moment standing there on the Sunnydale sidewalk and giggling to themselves. The demon's monstrous essence then entirely vanished from the material plane, never to return, just as if he'd committed a mental act of suicide. Frankly, Angelus was more than willing to return to his former residence in Hell, even if it meant an eternity of roaming around that nightmare dimension as just another ineffectual wraith, since anything else was far better than what he'd just horribly undergone!
Oddly enough, the disappearance of Angelus at last managed to attract his oblivious tormentor's attention, as that person in their colorful garb now glanced around in honest puzzlement, a perky snub nose scrunched up in cute bewilderment, as an actual sensation of something not quite right was now inwardly experienced by this individual. Well, that was easy enough to fix. In a truly sincere chortle that rang throughout the night, a high-pitched voice having in its tone the chimes of tinkling bells merrily appealed, "I wish for a happy ending!"