okay ive been playing for a while and i realized i didnt have all the convenants from the previous chapter and apparently im way too weak ( lvl 23) so does anyone here have a save code for chapter 3 where they have gotten all the covenants?
Getting all the covenants for the last chapter is impossible and intentional. The path splits between the Cat Guardian and infiltrating the palace through the door in the cave.
If you choose to infiltrate you have the option to meet Badluck again, who will give you one of his girls to fight and charm. You get a different fight and covenant(provided you charmed and didn't just beat the poor lass up) depending on which of your first two stats is higher.
You're level 23, so I'm guessing you've beaten the Cat Guardian of the palace, since she's the one who gives you enough EXP to get to lvl 23, lvl 22 is the max for Chapter 3 otherwise. I recommend sticking with her, her covenant gives the biggest bonuses and there's also the extra level thing.
If you still feel to weak, I recommend loading your save in Chapter 3(hopefully you can use the one where you have beaten the cat) and doing all the Alchemy in Irelia's shop, along with purchasing the two crystals she offers for 400 and 2000 orbs(if you haven't already).
Regarding the battle with Nyx, I just stayed with the Harpy covenant, slowed her down whenever I could and spammed Lightning. If she was resistant to it I used Groundswell instead. It took me quite a few tries, mainly due to the random nature of her attacks and resistances(the bonus items I got for watching the tutorial helped, so it's a good idea to do it), but I finally came victorious. Also, she seems to be an optional fight, so try and defeat her before leaving the room(there is a quest you can accomplish in it, giving you enough EXP for an extra level).