- Greninja reeks of cool... and then destroys its image with that tongue. There are so many reasons why that tongue is a stupid idea:
- It makes it difficult for Greninja to eat, speak or breathe. The tongue literally fills its mouth, and then some. Greninja can't even have all of it inside its body at any time.
- The tongue doesn't appear to serve any purpose but to "look cool". Which, given its impractibility, it certainly doesn't. It looks like Greninja ate one of those tongue-candies from Harry Potter.
- The soft tongue tissue has no place outside a creature's body. It would be too prone to wounds, and an easy target for enemies.
- It would be extremely prone to infections too.
All around, that tongue is simply the most ridiculously impractical body part ever conceived for a Pokémon. There is no excuse for it to be there. I know Greninja is based on some legendary thief with a red scarf, but if the scarf was so important, they could just... I don't know,
give it a f***ing scarf? Why does it have to be its tongue? Why not its vocal sac, or some loose skin flap, or an actual accessory à la Meloetta's (lost) shoes, Cubone's club/helmet or Spoink's pearl? Heck, if Gurdurr can carry an I-beam around with no explanation, I don't see why Greninja can't have a scarf. They better retcon it in some later generation.