Basically I had the idea that in the Pokémon world, there are sayings like how we have. Question is, what would some be? That's why this is here; for you to make up some (which, this could be especially helpful for free writers)! The only one I really have right now is "See you later, Feraligatr!", soooooo... we're off to the races!
Let's get the bad ones (AKA Mine) out of the way first~ "You're as blind as a Zubat." "Catch up Slowpoke" (Don't think it counts~) "Oh my Arceus!" "Oh my Helix!" "Don't Jynx us." And as quickly as I arrived... I vanish!
"That's about as useful as a tailless Magikarp in a splashing contest." I dunno. Some people in the Pokémon world might give criticisms like that. Feel free to use it (anyone) in a story if you have characters who would have such attitudes.
Oh, how about "Nuttier than Sentret droppings"? I used to hear that saying but with squirrels and more a profane word for droppings all the time from certain folks.
Team Rocket and their puns inspire me... "We've got something onixpected." "That is just onixceptable." "I'm having a blast-oise!" I dunno. Maybe something like "break the Regice" or "saved by the Bellsprout?"