Does the "The Perpetual Damage Machine" trick really work?

I suspect that this might be better asked as a "explain me the perpetual damage machine" with an answer by myself saying it does not work... feel free to put on hold if you think so too and I will reopen this in a couple days.

One infamous theoretical optimization trick has a character get dealt infinite damage while under the effect of spells, feats and/or class features that keep him alive and able to take actions, in order to get benefits based on the amount of damage taken.

The infinite damage loop, postulated by LordofProcrastination and used in both "the Omniscifier" and "Pun-Pun" builds, goes like this:

• The character manifests the share pain psionic power four times, on four separate targets.
• Then, by using the glory of the martyr spell from PGtF or BoED, take half the damage dealt to these guys, restarting the cycle.

I don't think this works for two reasons.

• The text of share pain clearly talks about transferring damage.

[...] the subject takes the remainder. The amount of damage not taken by you is taken by the subject.

It looks to me that there's some sort of "conservation of damage" law implied in the wording, and that it would not be possible to redirect the same half damage you're not taking to four different targets at the same time.

• The cycle just counts totals. You get dealt 8 damage. Even if we envision that 4 damage is dealt to each of the targets of share pain, each gives back 2 damage to the "main" character. This means that 8 damage generate 8 damage and the cycle continues forever. But I would rather say that each damage is counted separately and now share pain deals 1 damage, four times, to each one of the targets, and favor of the martyr halves that damage rounding it down, and the cycle ends.

Am I correct in saying that, RAW, the theoretical optimization trick known as "Dirty Trick #2: The Perpetual Damage Machine" does not work at all, way before involving any "drowning bug" to gain your infinte negative HP back ?

Theoretical optimization exercises like this often assume the best-possible rulings for any ambiguous rules. Share pain is not clear on what happens when you have multiple separate instances of it up at the same time—it might “make sense” for there to be some kind of “conservation of damage,” but the rules never say so, and for the purposes of theoretical optimization, that’s good enough.

In effect, the trick is built upon the premise that share pain can be used in this manner. The text of the power states that

You take half damage from all attacks that deal hit point damage to you,

and the attack in question dealt 8 damage. Nothing in the power is changing the amount of damage that the attack deals, which is the number the power uses here. It only changes the damage you take, which is not mentioned at all. So 8 damage is the “damage from [the] attacks that deal hit point damage to you” for all four instances of share pain.

The other consideration are the rules on combining magical effects. The four instances of share pain on the caster are each still present on the caster, but only one is relevant for him—that is, he only takes the half-damage once.1 But the other four targets each have only one effect on them—they need not concern themselves with combining magical effects. As such, they each continue to take the remainder. The fact that only one instance is “active” on the caster doesn’t matter because the effect isn’t described as sending the damage, it’s just split between them and just happens.

As for the separate instances of damage each being halved separately rather than being grouped, the argument stems from the exact wording of share pain: that it applies to “all attacks.” The damage from glory of the martyr isn’t an attack—but it is a result of the damage from share pain, which is a result of the original attack on the manifester of share pain. As such, that damage ultimately derives from the attack, and thus needs to be doled out per share pain. This is an even larger stretch than the previous claim.

But again, these aren’t hard-and-fast truths or the only way to understand these rules; this is the most favorable possible ruling. This is a theoretical exercise, not relevant to playing a game of Dungeons & Dragons.

1. Otherwise, he would take half-damage from each instance of share pain, taking twice as much damage as the actual attack dealt from four instances before *glory of the martyr even comes into play.
• Is there a reason the second and later manifestings of share pain add a share pain effect instead of cancelling the previous? That is, doesn't this simply run afoul of Same Effect with Differing Results? Jul 30 '16 at 14:09
• @HeyICanChan Ah, good point—that would, I imagine, be the argument against taking repeated iterations of the half damage yourself. You take one, because the effects, while still present, do not stack. The other targets, however, have only one effect on them, and are not concerned with combining magical effects: so they each take the reminder damage. This isn’t hard-and-fast truth, this is best-possible ruling, though. Jul 30 '16 at 14:19
• That is, indeed, the best possible reading. Splitting damage with a dude is the power's entire effect! It would take a lot of beers to convince this DM that the other share pain effects are left partially intact after the next manifesting of share pain. Jul 30 '16 at 14:47
• I'm sold on the first part. My second part was not "this should tick only once" it was "it should tick separately for each source" Jul 30 '16 at 22:28
• @Zachiel Addressed it Aug 3 '16 at 17:27