Everything beyond this rendition doesn't look like progress. This reads as a very soft pink pony staring with fascination at a firefly, outside and on a respectably light nighttime sky. Obviously it doesn't read as something real (there's no physical interaction (light and shadow!) between the firefly and the pony) but I don't feel that should. It's a rainbow coloured unicorn staring at a ball of light... fairly safe to say that realism doesn't need to be the goal.
Compositionally, the quoted version also works cleaner than the later renditions. The bands of colour in the hair direct you toward the eye where the visual tension between the firefly and its (her?) eye is set up. The only thing that irks me is the ear standing straight up and right on the edge of the frame. It creates tension that draws your eye to the ear, shows that the ear doesn't have a function in the composition (it points to nothing, says little and leads you nowhere!), and competes with the focal point for eye attention while not... yeah. It breaks things a little bit. I would greatly greatly greatly prefer it if the ear was lying flat back and breaking the edge of the image. If it were doing that, it could "point" to the eye and lead your eye inward from the edge of the scene towards where you're supposed to be looking anyways. It would also emotionally project an image of uneasiness or uncertainty at the strange thing in front of them WHICH feels consistent with the theme, to me.
As for the horn, I'd agree that it looks strange, but honestly a quick google search reveals that it looks strange on the "real thing", too. It only looks strange if you look at it, it isn't visually disruptive, so I'd say it can stay where it is and how it is without the world imploding.
