Angel finds a mirror that reflects vampires. Because of this, he ends up not helping with an apocalypse due to being too busy looking at his own reflection. Spike, however, does help, leading to Spuffy. Whatever other properties the mirror has are completely up to the author. This should be comedy/satire with traits exaggerated, unless it's something in the mirror preying on Angel's vanity and increasing it to the point where he can't look away, since he's not quite THAT bad in canon. Either way works. Have fun with it.