I am not Xander Harris, this should not happen to me!!
Someone who is not Xander Harris thinks it'd be pretty nifty to whip out his geekiness for Halloween, and since he is, once again, not a character in a teenybopper TV show he sees nothing wrong in mixing it up and blending characters and universes with his costume. After all, he lives in the real world, what could possibly happen?
Deciding to take a page out of a fanfiction story he once read, he actually writes a character sheet in which he puts down several changes to SB-Prime's Kryptonian race.
He chooses to mix Viltrumites, Kherans and Kryptonians to create a new alien race; one which has no vulnerability to Kryptonite( and even if they did, their Krypton had been vaporized by their star Rao, leaving no trace behind), whose main attributes are the same as those of a top tier Viltrumite, and whose other abilities are the result of extensive racial gene engineering and not dependent on the radiation of a specific type of star. To top it all off, they have managed to immunize themselves against magic.
What does happen is he wakes up in the post-Crisis, pre-Flashpoint DC Universe New Earth, with only vague memories of the previous night and facing a few pissed off costumed heroes.