Replace it with ... hit dice.
When someone hits you, you roll your hit dice to oppose their damage, risk-style.
Any dice that roll under the attacking dice are lost. If you want to be brutal, you then have to keep rolling any hit dice you have remaining until you beat each of the damage dice (you accumulate the HD rolls). (not just match, beat).
So if you are hit by a greatsword (2d6), they roll a 1 and a 7.
You have 3d12 HD. You get to roll 2 of them (no more than attacking dice) and get a pair of 4s. One beats the 1, the other loses to the 7.
In the brutal version, you have to keep rolling d12s until the 4 accumulates to more than 7, losing a HD every time the sum is under.
If you get hit by a fire ball for 8d6:
5,1,3,5,4,5,1,2
sorted:
5,5,5,4,3,2,1,1
you roll your 3d12:
2,12,7
sorted:
12,7,2
Your 12 and 7 beat their 5, 5, but the 2 loses to the next 5.
They have:
4,3,3,2,1,1
left. You roll your 2d12:
8,5
two wins!
3,2,1,1 left:
11,9
ok looking good, just two 1s:
1,1
oh no, you rolled badly:
1,1
you dead.
(Note: I used an online die roller for this. The double 1s on 2d12 happened!)
A side effect of this is that larger HD are more different than "bigger pool of HP", because a when you roll a HD and it exceeds the damage die, you keep it. So 2d6 HD might have the same or better average than 1d12, but will be more subject to attrition.
When someone hits you, you roll your hit dice to oppose their damage, risk-style.
Any dice that roll under the attacking dice are lost. If you want to be brutal, you then have to keep rolling any hit dice you have remaining until you beat each of the damage dice (you accumulate the HD rolls). (not just match, beat).
So if you are hit by a greatsword (2d6), they roll a 1 and a 7.
You have 3d12 HD. You get to roll 2 of them (no more than attacking dice) and get a pair of 4s. One beats the 1, the other loses to the 7.
In the brutal version, you have to keep rolling d12s until the 4 accumulates to more than 7, losing a HD every time the sum is under.
If you get hit by a fire ball for 8d6:
5,1,3,5,4,5,1,2
sorted:
5,5,5,4,3,2,1,1
you roll your 3d12:
2,12,7
sorted:
12,7,2
Your 12 and 7 beat their 5, 5, but the 2 loses to the next 5.
They have:
4,3,3,2,1,1
left. You roll your 2d12:
8,5
two wins!
3,2,1,1 left:
11,9
ok looking good, just two 1s:
1,1
oh no, you rolled badly:
1,1
you dead.
(Note: I used an online die roller for this. The double 1s on 2d12 happened!)
A side effect of this is that larger HD are more different than "bigger pool of HP", because a when you roll a HD and it exceeds the damage die, you keep it. So 2d6 HD might have the same or better average than 1d12, but will be more subject to attrition.
