Alright, I'll try
In that blurry image, there are 2 things that could be going on:
1) Obstruction: It is possible that it is just disappearing behind something else (that green thing on the right of it; perhaps an arm?). This seems the most likely case to me, and can be disproven if a clearer image is presented (or if someone can orove for certain that's the end of the tongue). What I see is the end of the tongue looking like this:
_____
_____I
When Greninja's tongue should be rounded, like so:
View attachment 173532
2) Proportion: As you can tell by comparing Greninja's ear or even the tongue around his neck, Greninja is pushed more towards the foreground in the blurred picture than the other image in your side by side. As such, it is possible that the shortened tongue is a result of the perspective from it being farther away.