Some great ideas in here, I really like this!
I was only thinking a few days ago that they should bring back Shadowskin as a baby TBN so I was surprised when I saw that it upgraded later on
I think the whole TBN/Blood Price interaction is a nice concept but just having up to 20% of your HP be un-healable would probably annoy the shit out of healers, I get that it's there to incentivize you to instead spend Dark Arts on it, but that just keeps the whole "only use TBN when you know it's going to break" problem, which I would personally rather just do away with- I don't like having mitigation tied to dps. Although, the healing from Red Wing would let you pretty easily heal up that damage you gave yourself, considering that each one is, at worst, a Bloodwhetting GCD. So maybe it'd be best to just kill the Dark Arts proc.
)