An obscenely funny Pokemon that will never happen.

This idea struck me as very funny! Mega Furret is a normal Furret of a normal length EXCEPT it's middle is plicated like an accordion that stretches to obscene lengths. Only one set of legs moves at any given time usually. The front legs move forward, the pokemon stretches out. The back legs move forward, the pokemon shortens back into normal length. In order to get somewhere quickly, Mega Furret uses both sets of feet at once. Sometimes, it bites its tail and forms a wheel to roll. As it walks, its body makes accordion noises. Normally it's just dissonant accordion noise, but the shiny Mega Furret makes MUSIC that speeds up or slows down depending on how fast the Pokemon is moving. It can learn music from other pokemon, trainers, television, radio etc!

a mega muk that just has a bigger body

Muk, but he doesn't fit in a storage container. Too big.

He cannot be too big, he is perfect

Muk, but he fits in an olympic swimming pool and eats yard clippings and compost, and he enjoys listening to opera and audiobooks.

What you’ve suggested here just reminded me of the slinky dog from Toy Story and now I want a Mega Spinda that’s like Mr. Potato Head because its spots fall off and the trainer has to reattach them all the time.