I've been going through similar, so I do understand.
One quick thing before getting back into looking over the set: the dark magic keyword doesn't work in black boarder as trample only applies to a creature's combat damage. You'd need to spell out "You may pay an additional <cost> to cast this spell. If you do, excess damage it deals to a creature is dealt to its controller or a planeswalker they control."
I've chosen to not use the trample idea. It's very hard to apply to a black card since black color doesn't do direct damage. So there isn't much use for it. I need to find another way to have a mechanic that can convey passing through defenses while also being faithful to black color's mechanics. It will probably still be called "Dark Magic" but how it works will be different. Probably something to do with life loss. Probably something like "You may pay an additional <cost> to cast this spell. If you do, target opponent loses (some number) life." I fixed the first line of the Dragon Acolyte's text btw. Thanks for the feedback on that syntax. I didn't realize I made that mistake.
If someone wants to also review the first Dark Souls cards by Jared McLaughlin that would also be appreciated. There's obviously some balancing issues with it. The only problem is, I would need to get the original images for the cards. Which may be hard to do. I recently noticed how OP the Bed of Chaos is. This will lead to unbalanced and unfun gameplay. You can basically create an exile deck that has this thing working in 2 or more turns. And then have a burn spell one shot an opponent player.