How this turn went down:
Enemy's hit roll: 19
My dodge roll: 18
Damage roll: 1
Damage: 8 (-5 Defense) = 3
My HP: 10/13 (/15)
Plan Attempt roll (torch): 18
Hit roll: 10
Enemy's dodge roll: 5
Damage roll (d6): 4 + (STRmod [5])
Damage: 9/-2 = 'healed' by 5
Enemy's HP: -15/0
Backstab's hit roll: 12 (+6 AGImod)
Enemy's Dodge roll: 16 (+4 LUCKmod)
Enemy dodges...
Just letting people know, these zombies have negative HP, this means that attacking it brings it farther away from 0, and thus, it would react as if you're healing it. Healing, however, and fiery attacks (which deal half their damage in healing Rot Zombies instead) will bring them closer to 0, and thus, they'd react as if they're getting hurt. If they reach 0, then they'll die, however, no amount of negative health will weaken it.