how do positoxins work?

[Ettina]

Positoxins are poisons that are only effective on corporeal undead, and explicitly bypass their immunity to ability drain or physical ability damage.

But what confuses me is that they call for a Fortitude save, and provide Fortitude save DCs. Obviously, they're bypassing the undead immunity to anything needing a Fortitude save, but how do you roll the saving throw? Or do undead automatically fail? (If so, why even give a DC?)

[animewatcha]

IIRC, the undead are treated as having a con score of '0' in this case. Whether this mean 0 as modifier or -5 due to crap con, I don't know.

[Necroticplague]

They simply roll Fort, just like anyone else. You could ask the same thing of when they get hit by a disintegrate. They don't have a con modifier to add to their save, but its otherwise the same as for everyone else.

Also, the undead immunity is to fort saves that don't effect objects, not fort saves in general (thus, why they are effected by disintegrate).

[Eloel]

IIRC, the undead are treated as having a con score of '0' in this case. Whether this mean 0 as modifier or -5 due to crap con, I don't know.

They have Con score of -, and modifier of 0 for anything relevant, iirc.

[Zanos]

Positoxins are poisons that are only effective on corporeal undead, and explicitly bypass their immunity to ability drain or physical ability damage.

But what confuses me is that they call for a Fortitude save, and provide Fortitude save DCs. Obviously, they're bypassing the undead immunity to anything needing a Fortitude save, but how do you roll the saving throw? Or do undead automatically fail? (If so, why even give a DC?)
IIRC, they don't actually specifically bypass the undead immunity to things which require fortitude saves and don't affect objects, so they don't do anything. :smalltongue:

A score of -- is treated as a +0 modifier. Undead should still have a base fort from HD or class levels, so you just roll that +0 from null con + any other bonuses to saves.

[RoyVG]

Specific trumps general.

Normally they would not need to make a Fortitude save due to being immune to poisons and anything else requiring a Fortitude save unless it targets objects (which poisons do not)

Positoxins are specifically made to hurt undead in a way a poison hurts a living creature, so they need to make a Fort save.