Credit goes to WolfDemon21, big thanks to JamesG for Poochpamp (Kimo)

Mercury and Kimo (the one instance he's not wearing him) were shopping at Kel and Leon's for supplies when Mercury happened to find a new brand of diaper, the brothers said it's designed to catch thives, but haven't tested it yet. Mercury paid extra to test them out and keep whatever he catches.
Kel and Leons obliged as long as he tells them.

Mercury not sure how it works decided to test it on his favorite diaper Kimo, Kimo got a closer look and pressed the button, before he knew it, the diaper captured him as it trapped him inside, Mercury enjoying this decided to test it further.

End

Kimo's new form in full body, kel and leon not sure who designed the diaper, but they do need testers which Mercury was happy to try.

Mercury belongs to Me
Kimo belongs to JamesG
Pokemon belong to Game Freak