I use GTS trading glitch to clone Pokemon and I also rip-off save data from the game cartridge and then use pokesav to clone the Pokemon.
Both of them are risky because with GTS trick, Pokemon you're trying to hack could be taken by someone and ripping save date off from the real game cartridge is pretty risky too because if you don't know what your doing, you could delete your savefile and even damage cartridge itself as it involves rom dumping method.
If you want clone, your best bet is to buy Action Replay because you probably don't wanna do what I do because of risks.