Two different kind of regeneration and vulnerability: what happens?

[Conradine]

If I have one talent that gives me regeneration except from fire and acid ( Troll Blooded from Dragon Magazine ) and another that gives regeneration except from holy and another kind of energy ( Improved Regeneration from AEG Evil )....

or any other kind of class feature, feat or whatever. So I take only subdual damage except from two sources, who are different.

In short, what happens?


1- I take only subdual damage because each regeneration protects me from the other weakness
2- I take lethal damage from each source
3- something else?

[Falontani]

the unfortunate RAW is that the Regeneration doesn't add together the numbers, but the weaknesses do stack. So it would be fire/acid/holy/etc with the higher regen number.

[Doctor Despair]

An easier method for immunity to most damage would be to take Half-Undead (Gheden), the LA +1 template that grants immunity to nonlethal damage. Then, take Troll Blooded (as you have) to turn all but fire and acid into nonlethal damage. Then, add a further template to get immunity to acid damage (e.g. Tainted Blood (Bestiary of Krynn, LA+1), or Void Mind, or Half-Dragon (Black)). Then, get the fire subtype (either by a ritual, or by paying a druid to cast Mantle of the Fiery Spirit on you). For the low, low cost of LA+2, a feat, and 16,200gp, you, too, can be immune to all damage except for fire damage enhanced as a Searing Spell. Add on a permanent or at-will flaming shield to reduce Searing Spell damage by half.

[ExLibrisMortis]

the unfortunate RAW is that the Regeneration doesn't add together the numbers, but the weaknesses do stack. So it would be fire/acid/holy/etc with the higher regen number.

To expand on this:

The general rule is that you take only nonlethal damage with Regeneration. If you have multiple Regeneration abilities, this is still the general rule (it can't really be anything else, can it?).
The exception is that certain types of damage deal normal (lethal) damage. If you have multiple exceptions (from multiple Regeneration abilities or otherwise), you take lethal damge from each of the damage types specified.

An easier method for immunity to most damage would be to take Half-Undead (Gheden), the LA +1 template that grants immunity to nonlethal damage. Then, take Troll Blooded (as you have) to turn all but fire and acid into nonlethal damage. Then, add a further template to get immunity to acid damage (e.g. Tainted Blood (Bestiary of Krynn, LA+1), or Void Mind, or Half-Dragon (Black)). Then, get the fire subtype (either by a ritual, or by paying a druid to cast Mantle of the Fiery Spirit on you). For the low, low cost of LA+2, a feat, and 16,200gp, you, too, can be immune to all damage except for fire damage enhanced as a Searing Spell. Add on a permanent or at-will flaming shield to reduce Searing Spell damage by half.

Favour of the martyr also provides immunity to nonlethal damage. Energy immunity (acid) and shapechange into a war troll completes the trick. Useful if one's campaign is more conductive to spell access (and persistomancy) than template shenanigans.

Fire shield provides immunity to Searing spells, due to the way damage gets multiplied together. There are still a few ways to get more damage multipliers, slightly reducing the utility of fire shield, but most people won't be able to touch you at all.

[Doctor Despair]

Fire shield provides immunity to Searing spells, due to the way damage gets multiplied together. There are still a few ways to get more damage multipliers, slightly reducing the utility of fire shield, but most people won't be able to touch you at all.

Could you expand on this a little bit? I basically see two ways it might work, but neither have that result, although I am presumable just overlooking something. Let's say a mage casts a searing spell attack that would deal 10 damage normally, and you are immune with a fire shield active.

1. The 10 damage is reduced by half based on your immunity (5), then reduced by half again based on your fire shield (2.5, rounding up to 3).

2. The 10 damage is reduced by half based on the fire shield (5), then reduced by half again based on your immunity (2.5, rounding up to 3).

I could only see it being completely negated if the reduction was treated additively rather than multiplicitively (i.e., both reduce your damage taken by 50%, adding up to 100%), but it surely doesn't work that way, right?

[ExLibrisMortis]

I could only see it being completely negated if the reduction was treated additively rather than multiplicitively (i.e., both reduce your damage taken by 50%, adding up to 100%), but it surely doesn't work that way, right?

It does, because damage is a game value, not a real-world value. "Half damage" really is -50%, just like Empower Spell is really +50%, not x1.5.

[Darg]

Half means half. It's not a multiplier. A 50% vulnerability with reflex for half is not 100% damage; it's 75%. It's the same thing with shield other: 150% split in half for 75-75 split. So fire shield (cold) would reduce damage to half, or 25% against a searing spell.

50% immunity is a multiplier though.

[Crake]

Half means half. It's not a multiplier. A 50% vulnerability with reflex for half is not 100% damage; it's 75%. It's the same thing with shield other: 150% split in half for 75-75 split. So fire shield (cold) would reduce damage to half, or 25% against a searing spell.

50% immunity is a multiplier though.

That's not correct though. A creature with vulnerability (+50%) that succeeds on a reflex save for half (-50%) actually does take 100% damage, not 75%, as per dnd's multiplication rules. In dnd, a half and a half is actually 0.

When two or more multipliers apply to any abstract value (such as a modifier or a die roll), however, combine them into a single multiple, with each extra multiple adding 1 less than its value to the first multiple. Thus, a double (×2) and a double (×2) applied to the same number results in a triple (×3, because 2 + 1 = 3).

So in the case of a double halfing, a half (x0.5) plus a half (x0.5) is actually zero (x0, because 0.5 + (0.5-1) = 0).

Meanwhile in the case of a vulnerability and a reflex save, you have a x1.5 vulnerability plus a 0.5-1 reflex save for half, meaning you get 1.5 - 0.5 for 1x damage.