Do what you feel is right. Don't force an ending because you think others would like it one way when you know it would fit better going in a different direction. Keep this question in mind: Will you tie up all loose ends or will you leave some unanswered for people to ponder over?

Uhmmm... I mean like... I've got the plot and I know the climax, but how to I finish it from there?

"And then they lived happily ever after"

Since I don't know the font3xt, I can't really give you any solid arvice

Advice

You know how you have chapter breaks or scene transitions? After the climax, I would just get to the next break and then stop writing. Make sure the characters are happy or contented (or sad if it's a downer) and then stop. If they have accomplished what they set out to accomplish, that should be sufficiently satisfying. Also (and this is good advice for any writing question) note how your favorite books end and do something similar.

Ok so... I've started writing the ending (I skipped the middle, it's actually better for people to write because if you come up with something u can put it in the start) and she's in a tournament with other "champions" with powers based off of gods. Christian God is a Mary Sue and has won a lot, Zeus and Odin are at eachother's throats, Hindu gods don't want any part of the violence, I need some other gods to take part in the tournament.

(Also, Satan is the main character's coach and I'm planning for her to kill Satan but what happens after that?)

Hahaha, I never write happy endings. I'm actually a Creative Writing major, so I hope I can help. Usually I have the endings planned before I even start, but I need to know a bit more first. Are you planning on writing a sequel? Do you want a happy or sad ending? Is your book funny? How long is your book going to be? Also, is the part where she kills Satan near the end, and is it supposed to be a surprise for the reader??

How do you feel about cliffhangers?

I dunno but I had my ending written out in detail before I even started writinf

Also be ready to change your ending in case you switch things up while writing the middle. I published a book of short stories and it was an almost constant process of rewriting.

Depends on the book

Ok so, while I was fleshing it out, Loki appears. He's gonna pretend to be Satan accepting the prize for the tournament. Protag shoots him, he's like "aw, ya got me" and then the real satan accepts his prize. But, what do I want to happen next?

Loki tries to kill Satan I guess

The end.

Loki is sad because he gets nothing in the end.
Ok then it has a little recap of what the world is like once Satan has won. Boom done

Book Two: Loki's Revenge? Am I pulling it too far?

"Book Two: Loki's Revenge" is essentially the basis of all Norse mythology so why not?

OMfg