Simply put, all you have to do is obey the rules of a previous Generation. If, for example, you pick Gen 5, you may only use Pokémon with abilities and moves released from that Generation. If you're wondering what the difference is between the actual Generation and the Bootleg, it's simple: all calculations and Pokémon are up-to-date. You can freely run Greninja with Torrent in Gen III as long as it isn't using unreleased moves.
Good luck (and don't get caught)!