Oh, my! Their stances and such additional action lines make it quite the display again! You can basically imagine their shaky movements here. Very exciting, Selphy! =D
It's no understatement. You sure have a nice way of presenting the action in a still image in a cartoony fashion. That shows your talent as an illustrator. I can basically both of them trying to read the situation here.

Char on the one side looks both like if he needs to test out if his big globe of a tum is not pulling himself forward but also much optimism. Nice way to picturize it by tilting his pose to the back slightly as if he's balancing it all out. Shiny did well with his pumping and the Charsune seems to enjoy his balloony tum.
I chuckle whenever I see Shiny in this particular panel because he somewhat reminds me of a Frog from this angle and with the big facial cheeks. You can well see that he's in a more critical position of the pump-off compared to his dude by how he's waving his arms and tries not to tilt onto his tummy that is nearly touching the floor. Shiny must feel quite bloated like one big beachball at that moment, Char seemingly is quite trained in pumping up toys. The Totodile can barely bounce his toetips up and down as his hide gets more sperical and pushes his legs apart into a starshape position.

All is still very neatly presented with carefully placed linework and a sweetly executed presentation. I enjoy it lots! =3