Onyx looks pretty happy for being defeated. :P
Not bad, if you added a little bit of extra animation for the Squirtle (like having him lurch a bit forwards or take a couple of steps), it would make it so the Onyx would actually crush him when he collapses. As it stands the Squirtle just disappears into a puddle of blood.
A few tweaks and this animation will be golden. Good work!