Willow was not happy. Nope, no happy Willows around, no happieness in Willow-land. The reason? Xanders costume. It was boring and dull and a typical men type of costume and Willow was absolutely against it. With her keen eye she started to scan the racks until... there it was, the perfect costume for him!
Xander balked. Willow weddled. He protested. She used the full-powerd resolve face. He tried to feebly argue against her choice. She used he most powerfull weapon against him: the Willow pout. A pouting Willow is a dangerous Willow and Xander folded, sighed and accepted his fate.
Later the evening, when she had just found out that she wasn't so coporeal anymore, she looked around and saw Buffy the noble lady screaming in fear and cowering from the demons. And Xander? She looked for him and blanced as she saw him smirking at her, before he turned into a barn owl and flew away.
She turned around and ran for it. Ran to Giles as fast as she could. Buffy's change was bad, really bad and the demons ands the other stuff was worse, but the worst was the carnage she could imagine Xander creating, in his guise as the Goblin King.
I proudly present Xander as Jareth the Goblin King, from the movie "Labyrinth.