On principle I utterly despise any and all single-player competitions that forbid a given Pokemon species. If you can't use Mewtwo against the game's high-level CPU enemies, then who the hell are you SUPPOSED to use him on?
Fact is, pretty much every Pokemon game requires getting the console version for an anything-goes high level battle. 2nd gen was somewhat better, with Red and all, but still.
Double Battles are awesome, though. R/S underutilized them, but that's why I love Colosseum (and to a lesser extent Gale of Darkness). And, to be fair, the Hoenn games had one awesome Victory Road theme (with an even more excellent remix in SSB Brawl).
Also on DeviantArt, Rumble, DLive.tv, and the Fediverse (@freespeechextremist.com and @bae.st)