What if by some strange turn of events, Superman and Batman had to take the showdown in a room emitting red sunlight? I believe that Lex Luthor didn't want to kill him with kryptonite bullets for it would be too easy. Also if I can remember during Smallville TV show and the Doomsday graphic novel he wants Superman alive to make clones of him and in turn have world domination in his grasp.
Kyptonite bullets? Come now, don't be rediculous. If those existed don't you think Lex Luthor would've done him in with him long ago? Plus SUperman would just move out of the way with his super speed. Batman's totally boned.
I visited superdickery.com and had a glimpse of the Showdown in Gotham City. Im curious as to wether you've read it or not as its struck my fancy. Surely Batman would get to use bullets made from kryptonite?