RE: PokeBeach's Official Ban List
What everyone else has said. Also, if you're not an idiot, you're not going to leave your Latios in on Mamoswine, you'll switch it out. Basically, every time you send in a Pokemon other than Mamoswine or have Mamoswine use a move other than ice Shard, that gives Latios a KO. And you're saying it can be handled fine in OU. Gotcha.
What everyone else has said. Also, if you're not an idiot, you're not going to leave your Latios in on Mamoswine, you'll switch it out. Basically, every time you send in a Pokemon other than Mamoswine or have Mamoswine use a move other than ice Shard, that gives Latios a KO. And you're saying it can be handled fine in OU. Gotcha.