According to Meowth346's summary page:Breeding with Ditto will not work.
Breeding with a female Swinub will have a half-and-half chance (my blue one is male). If the baby is female, it gets DV values from the father. Therefore, it would be shiny.
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"Normally, the earliest you can catch Mewtwo is 70. (Might be earlier on some carts)" - MewtwoSama, on Mewtwo's before-level-70 moves