Muffin is a shiny Mew which will be released when Pokemon Alpha Saphire and Omega Ruby comes out because of it's trainers moral code.

But it will die there. It was too long together with it's trainer and it won't adapt to the wild life in Hoenn. Please let us stop this cruel act with saving this poor little fellow. It needs a home and people who care about it. We need to make a Pokemon station outthere for Pokemon who got abandoned by it's trainer