Pinkie looks fine, no issues with her.
But your OC, his body looks a bit off, hard to explain. His mane and tail are a bit small, and while I'm not saying make them giant they don't mesh well and ponies exaggerate shapes and size, make them a bit bigger in scale so they match better but are still small comparatively to Pinkie's. Also their placement looks funny, tail should be up a little more, back back back more. And while him being a blank flank is probably either because no CM made yet or he doesn't have one, but the empty blank butt space is a bit jarring.
So, overall, not bad, Pinkie is perfect, but your OC needs a little work.