I've seen a lot of people asking for this in the game, but I'm going to ask for it too.

Exactly that, unicorn, pegasus and alicorn

And there is a difference that few people mention, the unicorn is an equine with one horn (I don't know exactly if it is a horse with one horn or an equine animal very similar to a horse) and he is not a magical animal and does not have a pure heart, he is an aggressive animal before being tamed and when killed his horn is used as a cup that nullifies any poison by people, pegasus doesn't have a horn, but it's a winged horse, it has nothing to do with a unicorn, they're different creatures, in addition to these, there is the alicorn/pegacorn/unipeg, which is a creature that is not real, it was only invented in literature and pop culture, it is a pegasus with a single unicorn horn.

That's it, I don't even really want these creatures but if they were added it would be cool if they didn't confuse the creatures because most games, movies and series do.