Protect your save

ACE codes write straight into the game's memory. It almost always works, but one wrong character can crash the game or break a Pokémon. These precautions save you a lot of trouble.

1. Save before anything else. Before the Mail glitch, before every code and before every trade. If something goes wrong, just turn the game off without saving and go back.
2. Keep Box 13 clear. Box 13 from slot 7 on, and every box after it, must be empty when you trigger a code. Never keep anything important in Box 13, slots 7 to 9.
3. Move the glitch species one at a time. In the PC, under MOVE POKÉMON, the Select button switches the hand to the mode that moves several Pokémon together. Don't pick up 0x0351 in that mode: according to the community, it disappears and you have to redo the Mail glitch. If the hand changed, press Select again and pick it up with A as usual.