I'm not sure if this will still be available, but I just read that the pearl pony has accidentally become available for breeding! This has been an accident and will probably b fixed quite quickly.
But if you have the pearl pony and it's still in your breeding list then use it with an other animal with 2 different elements to the pony and the odds of you getting a crystal unicorn is much much higher than previous chances. It's not an automatic guarantee but is a definite possibility. I got my second crystal unicorn when they made the land of the dead animals (skeletal stead and sugar skull glider) breedable to get the 3rd animal (dead wing) I got that pretty quickly so used my stead with its skull element to get my unicorn. I got it on my second attempt.
Hope this post was helpful!
(I feel I got a bit rambly!)
No, I'm afraid you can't breed with it . Because it has the unique element of zodiac it won't allow you to use for breeding.
All of my gem hybrids I have gotten through using my crystal unicorn and then an other standard animal that I have. I tend to use an animal with two elements as well as, although you will likely get more fails as outcomes, you can try for more than one hybrid if that makes sense? If not let me know!
Good luck on your zodiac quest!