Grammar
Color me surprised, but its pretty good. Nothing leapt out at me, so have your 10/10
Good job.
Style

It's decent. At times its actually good, with smooth flow and great descriptions, at time somewhat stilted. The only thing that spoils it for me is the edge.
The author says that the idea has been with them since they were 14,and it kinda reads like that was not that long ago.
There is this anime-esque edginess there that just seeps through. Just how much his OC windigoes are cooler than normal ponkes (pun not intended), how really edgy their leaders are.
Show, dont tell, my dudette.
That also applies to the overabundance of exposition in the text. You wanna dose this stuff carefully - the readers probably want tk have a story, not a wiki on how cool your idea of Windigoes are.
Finay short chapters. Less than 1.5k is way too short if you ask me. It can work in some formats, but consistent short chapters arent great for long adventure stories. The industrial standard is 3-8k.
So far the style is the weakest part of this work. I give it maybe 12/20.

Plot
Eeeh...its not terribly original, but its too early to tell.
Some elements (use of Cutie Map, awesome (at least allegedly) princess, few other things), give me hope that this is not "my badass awesome edgy OCs beats up namby-pamby ponies and/or marry Mane Six" story, and it also doesnt seem to be "teach them ponies how manly men solve problems with their fists" territory, so, I think it has some promise.
I, for one, want to see where it goes.

Otherwise, less than 6k into the story is too early to tell. We dont get any characters yet, except couple of lines from Twilight and Rarjty or an expodump from Spear Carrier No15, nor has anything reay happened yet.
Have yourself provisional 25/30, under the assumption that before writing next chapters, you're gonna watch a little less anime and pick up a proper book

Overall
Author has a story to tell. Their own story, not quite the fifty-seventh rendition of Coolio McEdgerson in Equestria. There are some ideas on world building, some plot, decent character work - all showing good potential. I like this work, and I'm gonna track progress.
8/10.

Total
55/75 - 73%
You got a story mate, now all you need is write it.
Go get 'em, tiger

7679836
Aww tysm, I really appreciate it. Its been on a standstill currently due to college being a mess lol.

Also, my pronouns are she/her, fyi.

Tysm once again, I'll take your advice moving forward, and will re-edit my older chapters. I'm still struggling with the show don't tell aspect of a story, and how I have a habit of condensing the words rather than stretch them out, so I especially am glad for you making me aware of that, in addition to the other criticisms. All in all, I hope you have a wonderful day! ♥️