The difference between Classic Hackmons and Blanced Hackmons is that, in Balanced Hackmons, there are banned moves and abilities. Classic Hackmons is a free-for-all, anything goes format (Huge Power Regigigas, anyone?) However, the metagame was stabilized and made a bit more fun by banning a few things. The current Gen VI banlist is as follows.
>OHKO moves (Sheer Cold, Fissure, Horn Drill and Guillotine)
Shadow Tag/Arena Trap
Evasion moves (Double Team, Minimize, etc.)
Endless Battles (see FunBro)
(Also, if I remember correctly, Imposter Blissey is also banned)
Nicked it from here.