Your Oc is A mary sue, but if your Oc is a Alicorn that doesn't mean that's the reason for it. Try to think about your BIO and how it works with the show cannon and take it by some friends if you want.
Here is a little definition
A Mary Sue is an idealized and seemingly perfect fictional character, a young or low-rank person who saves the day through unrealistic abilities. Often this character is recognized as an author insert or wish-fulfillment.
Also, Don't let people tell you the reason your Oc is a Mary sue is because its a alicorn and it has rainbows because that's not always the reason but some times it is
Good luck with creating!
