Here's the entire unicorn. She's not very large in this cel, but the cel came with the background that the seller said might be from film. I took a chance since I didn't have a whole unicorn anyway.
I haven't been able to ID the background from the movie though, so I may have guessed incorrectly. The background looks like something Topcraft could have done though. If you see the background in TLU or elsewhere, I'd be grateful if you could let me know where you saw it.