Couple of things I noticed outright:
1. The poners should have a bit of a curve before the connection to their heads. As a greater drawfag than I once informed me, poners don't really have to have necks but if you don't taper them off a bit then it won't even give the illusion of it.
2. Twilight's hoof doesn't really seem like it's wrapped around filly, just kind of loosely floating behind her. This works in the other image because humans are capable of standing on their own, but poners aren't capable of this feat for much longer than a few seconds.
3. No real complaints for filly's head other than maybe adding nostrils (that's a stylistic thing though) but something seriously uncanny is going on with Twiggy's head. Be sure to only follow the pic you're trying to parody in general form, not anatomy. The mouth of the horse should at the lowest
directly beneath the base of the muzzle. The muzzle itself should also be tilted so that we can see the side as well as the front at that angle. I don't really know how to describe it better than that, sorry.
4. Twiggy and filly should probably have slightly larger ears.
5. Thick legs are very important to the cuteness of a poner. Many people make the mistake of thinking that they're a lot like human arms and legs in thickness, but you really want to go thiccer.
5. Adding a dock to filly could help, but since the show doesn't really do docks I see them as stylistic. You do you there.
6.At that angle, you really shouldn't be seeing the line for Twilight's right leg (right from the perspective of the viewer, btw.) her butt should be obscuring more hf her leg.
7. Line for the left leg ends a bit lower, hemispheres are good but you generally want to integrate them a bit more seamlessly into the rest of the poner.
8. Twiggy's horn should be poking through her mane.
9. Never underestimate the power of cutie marks. They just generally look nice, and leaving them out is generally no bueno imo.
I like the concept, hopefully you can use some of that to improve upon your drawings. And maybe draw more anonfilly.