You're welcome
I don't think there's a way to cheat out the remix bosses. I think the stats are build in the game itself and not in the save. Or maybe it's possible to find a glitch to keep our knight level XXX for the fight, I dunno but I doubt.
Whatever, those bosses are a pain in the ass but if you keep going, it's possible. The only very difficult fight is Alexander IV 'cause it's mostly based on luck.
For Khidr, you must learn his parterns and if possible NEVER stay on the platform above, always below, this makes it easiers to avoid tears.
Ponce de Freon, once you get how he works it's simple just do a big ∞ below then jump above and try also to do a small ∞ so that the fireballs above can start disappearing.
Alexander IV: Mostly luck but it happens that when he comes without any of his kids, so it becames pretty simple. For that, block him in the right or the left corner then teleport to the opposite side (very very opposite, don't forget to put ur shadow) and if he doesn't come, jump near the picks and go back to the platform. If you're lucky, he's gonna come all alone.
The two others are pretty simple.
Ponce de Freon :
https://www.youtube.com/watch?v=3KcKJEuN334
(with this vidéo I succeed in 20 tries more or less).
Alexander IV:
https://www.youtube.com/watch?v=yn1lMrZwu7U
Just do like he does and you'll surely get this "bug" when Alexander comes alone, it helps a lot and if you can't avoid him, jump on the spikes, less damages.
Hope it can help.