Immunity to Disease is making things immune to all the damage from attacks

[Affirmatron]

Tested on a clean install (no modules ever) of version 6.9.0 of the PF2E system and version 12 stable build 331 of Foundry itself.

The issue is that when damaging a creature with the 'disease' immunity, they take no damage from the attack with that trait - ie slashing damage from a leukodaemon's claws. To repeat this issue select a creature immune to disease, such as an urdefhan lasher, and roll the damage from an attack with the disease trait, such as a leukodaemon's claws, and then try to apply it.

The rules for Immunities found on page 408 of Player Core state, in part:

START OF QUOTE FROM BOOK

If you have immunity to effects with a certain trait (such as death effects, poison, or disease), you are unaffected by effects with that trait. Often, an effect both has a trait and deals that type of damage (such as a lightning bolt spell). In these cases, the immunity applies to the effect corresponding to the trait, not just the damage. However, some complex effects might have parts that affect you even if you’re immune to one of the effect’s traits; for instance, a spell that deals both fire and acid damage can still deal acid damage to you even if you’re immune to fire.

END OF QUOTE FROM BOOK

I did the bolding.

This means that a thing that is immune to fire, but has the unholy trait, is not immune to the spirit damage from Holy Light but is immune to the fire damage. I tested this and it is the case in the system, giving a leukodaemon immunity to fire and zapping it with Holy Light did in fact apply the spirit damage properly (including the weakness to holy). Removing the weakness doesn't stop the spirit damage from happening and nowhere in the rules does it state a weakness would interact in that way (abrogating immunity in a Specific>General sort of rules-check) but I tested it anyway.

I believe this should mean that something immune to disease should still take the damage from, at least, attacks with the disease tag as the disease is an afterthought because their gross claws or whatever introduced it into your system. In other words, such an attack is a 'complex effect' that has the disease trait but has parts that affect you even though you can't get a disease.

A spell that does bludgeoning damage because it infects you with rapidly growing cancerous tumors, however, maybe not since the damage is coming from a disease? So I accept that this is maybe a more complex issue than merely standardizing whatever was done with fire, since there's no 'disease' damage type.

[stwlam]

It's difficult to parse this out since your quotations aren't demarcated, but applying the example you're citing would have disease be a damage type, which it isn't.

[TMunsie]

The core of their problem is that the strike is tagged with the disease trait, so a creature with disease immunity is taking no piercing damage from the attack. They’re arguing the piercing damage should go through and the trait refers to the secondary effect, which a disease-immune creature should be immune to.

Effectively the ask is to remove “disease” immunity as a trait from being propagated to non-disease portions of an NPC strike.

It’s bad Paizo editing/poor use of inheritance but is also opposite to how we handle every other trait. RAW the strike is immune because the strike has the disease trait (what we implemented) on the damage but RAI there is no reason why the piercing damage wouldn’t affect a disease-immune creature.