Sides, the list of what can't be used in random matchup is right here:
Mewtwo, mew, Lugia, ho-oh, celebi, Kyogre, groudon, rayquaza, Jirachi, deoxys, chatot, Dialga, palkia, giatina, Phione, manaphy, darkrai, Shaymin arceus, victini, Reshiram, Zekrom, Kyurem, Keldo, Meloetta, Genosect.
And for some reason, Chatot is banned too.
Copypastaed directly from source.
Edited by Runner, 02 June 2011 - 07:13 AM.