looks tits, ur making it complicated with worlds don't u have any brain at all ?
Maybe if Someone... ask R to make a world named "Challanges world" ( or something like that ) to be locked, and only in case of some matches Admin can set who will be in there, after the match admin would set those ppl who were in match not to be able to enter that world again ( in case of abusing )
erm Mike I won U once in that kind of matches, i think that is originaly were u got the idea
it was 3:2 if I rember good?