Repeat after me: "Skill rebalance". Now tell me how does "skill rebalance" pertain to not being enough of some type of item. A bunch of buffs, because if armour penalty scaled with your skill tree's progress, people would want a smoother progression than "-5, then -2". Either way, you'd still have to place triggers on every piece of heavy armour in the game, both basic and all expansions, and in mod-added pieces of heavy armour too. So the solution, while possible to code in, if far from elegant. Every skill tree, because otherwise crossbows' critical hits would work normally and not the way you propose them to if you didn't have that particular skill. And just end it. We can already see that your idea will get very convoluted before you even get near where you want to be. Just take "we can't do it with the hooks we have now" as an answer and if you really want that change, go to the suggestion area and write about that to Nicholas as he's pretty much the one who can add hooks we would need. Spoiler: But for those who really want to know: You'd need two triggers, one a crossbow trigger that would have to be activated first, and one a critical trigger. Crossbow trigger would give you a buff that would disappear at the end of your attack. Critical trigger would activate the desired effect (two triggers, one activates the "buff" you want, and the other activates additional attack effect that scales with EDR) and remove the dummy buff at the end. But that is a shoddy solution. Erm, what? I think it's more about people thinking of different "blood magics". There are some fantasy settings where blood magic pertains to souls rather than blood, and the one I see here is a mishmash of both concepts. Not that it's bad or anything, since the skill trees are supposed to be more about theme and mechanics rather than matching some particular definition of what something is.