Curse of the putrid husk vs. Elemental

Question

In a recent game a spellcaster cast curse of the putrid husk at a fire elemental.

The spell reads

Illusion (Phantasm) [Fear, Mind-Affecting, Evil]

Level: Brd 3, Sor/Wiz 3
Components: V, S, M
Casting Time: 1 action
Range: Close (25 ft. + 5 ft./2 levels)
Target: One creature
Duration: 1 round + 1d10 minutes
Saving Throw: Will negates
Spell Resistance: Yes

This illusion forces the subject to believe his flesh is rotting and falling off his body, and that his internal organs are spilling out. If the target fails his saving throw, he is dazed (and horrified) for 1 round. On the following round, he falls unconscious for 1d10 minutes, during which time he cannot be roused normally.

Now thinking of a fire elemental it doesn't have organs or flesh as it is comprised of fire, but reading the fire and extraplanar subtypes and the elemental stat black it was ruled that the spell technically still worked.

Is this just something that is mostly up to the DM or are we missing a rule somewhere?

Answer 1

Narrating the Story is up to the DM.

The spell effects operate as stated. The interpretation of the stat blocks was correct. What the elemental interprets as "his flesh is rotting" and "his internal organs are spilling out" needs to be sorted out by the DM.

Answer 2

This depends on whether the DM wants to go the Rules route or the description route.

If he wants to go the Rules route the spell will still work, but maybe he'd "animate" it as the fire elemental becoming ashes and a waning flame, causing it to be terrified (or maybe he's freezing?.) That said, explaining that to the players would also no make sense, as they can't perceive what it thinks. Regardless, this is Raw and Rai but it also is likely to cause some laughs at the table. This would be the "40k poison" ruling; where Poison is assumed to work on Necrons but not vehicles, Nurgle units but not a soul grinder, etc; just because you only care about the rules interactions.

If he wants to go the description route, he may just say that it automatically fails because the spell effect doesn't make any sense. Maybe the elemental sees crazy rot happening to its body but it makes so little sense that it can't be scared of it?

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If you'd like the spell to work, you may point out that you're just causing a fear illusion and that the description is catered to regular mortals and that the DM shouldn't punish your spell choice just because he chose a weird monster for you to fight.