My headcanon for greninja is that official art greninjas are like pokemon super-models and every greninja you see with a trainer is kind of chubby like this because they keep using their AWESOME NINJA POWERS to sneak snacks.

My least favourite part of greninja's design is its stupid codpiece of justice because it's difficult not to make it look like bits of one sort or another if you're using sepia-mono-chromo-tone-o-vision like I do often.