The cloning glitch in Gold and Silver probably. In Gold and Silver if you deposit a Pokemon into a box, then switch boxes, and then turn the power off in the middle of the saving process before switching boxes, you will have a clone of the Pokemon you deposited. I'd take advantage of this glitch by cloning Pokemon I really wanting to have second versions of , mostly legendaries. My friend would also use the glitch to clone Lugia from his Silver and he would trade them to me so I could sue them on my teams to beat the E4. Never really got a legit Lugia in my Gold version, lol.