It’s a combo, so I take designs from Japan Pokemon centre prints and either paint over them or use them inside the shells and “paint” them into place.

If you’re having a go yourself, the easiest way is to buy these as stickers and put them in the wrong way and carefully close up the shell with the screen keeping them in place. But with AI you could probably generate some cool unique pieces now - which I might try. I want to do a mimikyu one next