It's harder than I expected:
You need 3 pkmn in total, the first is your newly bred pkmn with mimic tutored in emerald but without selfdestruct (let's say snorlax for example), the second is a smeargle with selfdestruct, double edge, curse, counter and the third is a ditto with transform.
Enter a double battle with ditto first slot and snorlax 2nd slot.
Turn1 - use transform with ditto and counter or bslam or dedge with snorlax
Turn2 - use a potion with ditto's turn and let snorlax mimic ditto
Turn3 - switch ditto with smeargle and make snorlax use transform on ditto (it'll transform to a smeargle)
Turn4 - switch the smeargle with any other poke and finish the battle without switching snorlax (you can even use selfdestruct so it faints with the opponent's pokes and it won't gain exp)