Does the DR 2 / Cold Iron come into play for a sprite swarm when they have weapon immunity

[Rogar Stonebow]

Just a quick question. My Brain has stopped working some time ago, but I was looking at the sprite swarm, and for Defenses they have DR 2/Cold Iron, Immune weapon damage. Does the DR 2/Cold actually come into play if they are immune to weapon damage anyways?

Also, If I were to make them into an undead sprite swarm, what would their DR look like? What would their CR rating be afterwards?

[The Black Bard]

There are a few ways to do area of effects that do physical damage (Ice Storm), so the DR would apply.

I believe there likewise might be a few ways to do area damage that is also cold iron, but I can't recall which specific spell it might be. Brain fail.

[Rogar Stonebow]

The Black Bard wrote:

There are a few ways to do area of effects that do physical damage (Ice Storm), so the DR would apply.

I believe there likewise might be a few ways to do area damage that is also cold iron, but I can't recall which specific spell it might be. Brain fail.

I see, so then emptying a large bag of cold iron caltrops into them would work as well?

[Deighton Thrane]

The DR would still apply on an attack from a character using a Swarmbane Clasp and a non cold iron weapon.

[Avoron]

A normal pellet grenade would get impeded by the DR, and a cold iron one would bypass it.

[ShieldLawrence]

Kineticists can attack swarms at full effectiveness but the DR would apply to their physical blasts.

[SorrySleeping]

Rat Catcher allows anyone to hit swarms with physical damage.

[blahpers]

As for undead, depends on the template. Look up templates like skeletal champion, zombie, lich, and so on and apply as normal. DR will depend on the template applied--for example, skeleton replaces existing defensive abilities with DR 5/bludgeoning, while with skeletal champion the swarm would have both forms of DR, applying whichever is most advantageous against a particular attack.