How can you inflict % HP damage in GURPS?

[whswhs]

Setting aside the question of whether it CAN be done, there's a question of what effect you have in mind for "total HP."

Consider a human with 10 HP. That represents the damage needed to require them to roll to see if they remain conscious. But the amount that requires them to roll to see if they die is 20 HP (taking them to -10 HP). And the amount that kills them for sure is 60 HP (taking them to -50 HP).

If you inflict half of 10 HP, or 5 HP, that's a major wound, but it has no chance of killing them, or even knocking them out. If you inflict half of 20 HP, that's 10 HP, which requires a roll to see if you knock them out, but still won't kill them. If you inflict half of 60 HP, that's 30 HP, which takes them to -20 HP, so they have to roll for unconsciousness for being at or below 0, and to roll to see if they live when they reach -10, and again when they reach -20.

Which of those levels do you want?

Also, say, for example, that you go for the first option. Your target has 10 HP; you hit him for 5 HP. Now he has 5 HP left. You hit him again. Do you do 5 HP again? Or do you do half of his remaining 5 HP? That woulld round up to 3 HP (if you round down you can never get him to 0 HP!), so now he has 2 HP. Half of that is 1 HP, and now he has 1 HP. Half of that rounds to 1 HP, so now he's at 0 HP. If you do it that way you kind of nickel and dime him down, and I'm guessing that's not what you want. . . .

[Varyon]

No Wounding is -60%. Personally, I'd multiply that by the percentage the Injury (not damage) is capped to leaving the character at (25% Injury leaves the character at 75% HP). So, 25% Injury is -45%, 50% Injury is -30%, 75% Injury is -15%. You still have to purchase the relevant level of damage as an Innate Attack, however. For example, let's consider an attack that halves the target's HP. We'll call it Demi.

Basing it on Crushing Innate Attack, we'll first give it No Blunt Trauma and No Knockback, for -20%. It gets another -30% for being capped at 50% Injury, for a total of -50%, or [2.5]/level, assuming no other modifiers are in play. Each level averages 3.5 damage, and as we don't want to bother with rolling, we'll mark it as average.

A character with Demi 4 [10] does 50% current HP Injury on unarmored foes up to 28 HP. Against a foe with 100 HP, he still only deals 14 Injury, because that's all he paid for. To fully affect such a foe, he'd need something like Demi 15 [38].

Note such an attack has a huge benefit - so long as bleeding isn't involved (or is weak enough for you to stop, and with such an Injury cap it probably is), you can use it to harm and weaken a foe without any real risk of killing him. Blast away until the foe is below 1/3rd HP to make them much easier to capture for later interrogation. A big disadvantage is that, at or below 50% Injury cap, it's literally impossible to cause a Major Wound, although there are other ways to trigger that knockdown/stun roll (crippling extremities, or targeting the Skull, Face, Vitals, or Groin).

Note here I'm assuming you are defining "total HP" as "remaining HP above 0," as your example strongly implied.

[AlexanderHowl]

No Wounding is -50% (Characters, p. 111). If you want an attack that cannot do damage after a living target suffers a certain amount of damage in order to prevent death, then that would be workable. I would give an attacked capped at -(HP) a limitation of -10% while an attacked capped at 0 HP would receive a limitation of -25%. I would restrict the limitation (which I would call Merciful Attack) to attacks that deal only Toxic damage though, as it would be meaningless against nonliving objects. If the effect was optional, it would be an Enhancement worth 25% at the 0 HP limit and 10% at the -(HP) limit.

[kirbwarrior]

Originally Posted by ericthered

You could probaby do something with the heart attack modifier on affliction. That kills outright. The target gets a resistance roll though.

I've done that myself to imitate Demi from Final Fantasy. My initial build was to make it a variant of Heart attack; You drop to -1*HP as per Heart Attack (and I think it also affects FP), but you don't die. However, the attack is instant (Heart Attacks take minutes to actually kill) and it gets around No Vitals.

My lesser version was I think 150% to take out half the HP difference from current HP to -1*HP.

To get around resistance checks, bring up the Affliction level to something like 20 and add the limitation "Only on living things" so you never have to worry about the power being used on something like the planet.

Trying to do it with IA doesn't work well since there will always be a cap on how much damage you can theoretically do.

[Balor Patch]

Affliction IT:DR (2) cumulative duration(normal healing)

Price the reversed IT:DR and the duration to taste.

[Varyon]

Originally Posted by AlexanderHowl

No Wounding is -50% (Characters, p. 111).

Oops. I was going off of memory, and while I remembered that nbt+nkb+nw was -80%, I had thought that No Blunt Trauma and No Knockback were -10% each, but checking it looks like they are -20% and -10%, respectively.

Originally Posted by AlexanderHowl

If you want an attack that cannot do damage after a living target suffers a certain amount of damage in order to prevent death, then that would be workable.

That's how the ability Hide described works.

Originally Posted by AlexanderHowl

I would give an attacked capped at -(HP) a limitation of -10% while an attacked capped at 0 HP would receive a limitation of -25%. I would restrict the limitation (which I would call Merciful Attack) to attacks that deal only Toxic damage though, as it would be meaningless against nonliving objects. If the effect was optional, it would be an Enhancement worth 25% at the 0 HP limit and 10% at the -(HP) limit.

I see no reason to restrict it to Toxic - the Limitation isn't any degree of realistic to start with, and I can easily see cases where the attack isn't able to break objects either. Also, I'd personally be tempted to put those Limitations at -5% and -10%, respectively, because with rare exceptions getting a foe to or below 0 HP is incredibly useful, and being able to do so with no or little risk of killing even more so (it's still a Limitation, of course, as it makes those few foes who manage to stay standing more difficult to deal with). The Enhancement values sound fair, however.

Originally Posted by Balor Patch

Affliction IT:DR (2) cumulative duration(normal healing)

Price the reversed IT:DR and the duration to taste.

That's something that makes the target simply take half injury (or 1/4, or 1/18, etc, depending on how many uses you've stacked) from all attacks, and does absolutely nothing to restrict injury to a certain fraction of the target's HP. I also don't know what you mean by reversed IT:DR, unless you're referring to Vulnerability, but that would simply make all attacks do more damage to the target.

[lachimba]

Originally Posted by Hide

Hello!

I would like to create an innate attack which reduces a percentage amount of HP if successful. For example, "always deals 50% of the available HP as damage". So, if you have 100 HP, first you deal 50 HP damage, then 25 HP damage, then it would be 12 HP damage, and so on...

I haven't found anything like this yet, what do you think?

Thank you!
- Hide

Is this for a PC?


No, then just do it ignore the rules.

Is it for a PC?


Keep reading this thread.

[Varyon]

Originally Posted by lachimba

Is this for a PC?

No, then just do it ignore the rules.

Of course, even if the ability doesn't belong to a PC, sometimes a point value is needed. The +300% version of Power Theft on Neutralize (P50) uses the point value of the relevant ability/abilities. Additionally, characters with the ability may be Allies or Enemies. Summons are also a potential issue - Planar Summons and Summon Demon, at least (don't have Magic, so can't check other summoning spells), base their cost on the point value of the summon, and summoning spells in RPM and Sorcery are both based on Ally.

[lachimba]

Originally Posted by Varyon

Of course, even if the ability doesn't belong to a PC, sometimes a point value is needed. The +300% version of Power Theft on Neutralize (P50) uses the point value of the relevant ability/abilities. Additionally, characters with the ability may be Allies or Enemies. Summons are also a potential issue - Planar Summons and Summon Demon, at least (don't have Magic, so can't check other summoning spells), base their cost on the point value of the summon, and summoning spells in RPM and Sorcery are both based on Ally.

Ok based on a PC or ability that requires it.

Ive lost count of the number of threads that are about using "complex" maths to do something the players will never see.


If a monster needs to do percentage damage then it does.

[Kromm]

One way to look at things:

Unliving objects have twice the HP of living ones. Homogenous ones have twice the HP of Unliving ones. Injury Tolerance (Unliving) is 20 points; Injury Tolerance (Homogenous) is 40 points. So roughly speaking, each doubling of HP corresponds to a 20-point trait. Now of course those traits don't actually affect HP, but we could posit that removing them from an object that has them would temporarily make it flimsier, so we could imagine that's Affliction with Negated Advantage, +20%, but we could call it Hit Point Reduction, +20% instead.

Normally, that would work just once, so if repeated uses stack, that's Cumulative, +400%. And duration is normally minutes, so if it's "permanent until healed," that's Extended Duration, Permanent, +150%.

There would still be resistance rolls aided by DR; to remove the effects of DR, add Cosmic, +300%.

So for 97 points, you could have an attack that cuts HP in half, round up, if the target misses a HT roll. I'd say it affects current positive HP; at 1 HP or below, it wouldn't do anything. Thus if a fighter with HP 16 were currently at 13 HP, the first zap would make it 7 HP, the second zap would leave 4 HP, the third would leave 2 HP, and fourth would leave 1 HP, after which nothing would happen.