Hello there,
Can you share more details for your shiny Regigigas? Such as, if it's in English or not, what game/region it was caught in, what IV's it has (if you know of any), moves, Nature, etc.? I have a shiny Docile Lugia (that I think has 2 IV's, but I'm not 100% certain on that), Hoenn-born (from Alpha Sapphire) that I'd offer in return for it. Someone else that I'm trying to help out a bit is looking for a shiny 5/6 IV Regigigas.
Looking forward to hearing back from you!
Trainer name: Nick Ketchum | Friend Code: 3050-8204-5112