So whenever I shiny hunt for a legendary, I typically like to have another one that is not (Just because I'm like that). I remember back in 4th gen, there was a code for making all legendaries reappear, and to my knowledge that isn't possible for USUM or any other 3DS pokemon game. So What I typically do is use JKSM or checkpoint to do so, this is a fairly simple thing to do, and probably doesn't even need to have a step by step, but I'll do so anyway just because.
1) Go infront of your wanted pokemon before encountering it or receiving it (legendary or pokemon like the surfing pikachu) and save
2) Then go to your save manger, I personally use checkpoint and make a backup
3) Go back to your game, catch the pokemon, then save.
4) Go to either PkHex or PKSM and save it. I usually put it into the bank on PKSM.
5) Restore save
6) Go back to your save editor and put it back into your PC or wherever
7) Profit. Now you can have the normal version and a shiny version or whatever thing your trying to get on it.
So yeah pretty simple, but is really helpful for me personally and is really helpful for getting multiple natures of a pokemon legitimately (well kind of)
1) Go infront of your wanted pokemon before encountering it or receiving it (legendary or pokemon like the surfing pikachu) and save
2) Then go to your save manger, I personally use checkpoint and make a backup
3) Go back to your game, catch the pokemon, then save.
4) Go to either PkHex or PKSM and save it. I usually put it into the bank on PKSM.
5) Restore save
6) Go back to your save editor and put it back into your PC or wherever
7) Profit. Now you can have the normal version and a shiny version or whatever thing your trying to get on it.
So yeah pretty simple, but is really helpful for me personally and is really helpful for getting multiple natures of a pokemon legitimately (well kind of)