Hm, are you sure you want 16 damage at 50 HP with no max HP modifiers? I was trying to get a more noticeable risk/reward bonus. Mine was pretty weak, now that I look at it. I thought it would be interesting to have it would be weak until HP is clearly risky (maybe 30% of HP remaining). I came up with this:
(MaxHP-HPLeft)2/400
Stupid Shard of Sacrifice though. At 20/100 it deals 16 damage, and at 80 it deals 1 damage. And 50/100 would be 6. Meanwhile 50/499 (Stone Skin stall) would be -never mind, too high. Maybe an exponential equation?
301-( (hpLeft/maxHP) )
That gives the Stone Skin an extra HP flexibility, but max damage is still 30.
Okay I think the second equation is good now.