I think I figured out how to build Supernatural Durability out of spare parts

[Nereidalbel]

Originally Posted by Anthony

Mechanically speaking, the correct way to do supernatural durability is probably to just to make the character invulnerable to attacks doing less than HPx10, and then apply limitations for "still sort of vulnerable".

Being dropped below 0 HP still affects a character with SD, though. Their specific weakness can force death checks as normal, meaning it's worth tracking HP loss down to -5x HP.