Help me find the right Unico plz!

So I'm trying to find this for my girl. She was telling me she used to watch this when she was a kid. She told me about her favorite one, and the only thing I remember is:

Unico jumps into the ocean (or a river or something) and comes out as a big Pegasus-like unicorn.

I also remember her saying something about a devil.

Any help?
Thanks