The (legacy) sibriex (Mordenkainen's Tome of Foes page 137) has the following trait:

Contamination. The sibriex emits an aura of corruption 30 feet in every direction. Plants that aren't creatures wither in the aura, and the ground in it is difficult terrain for other creatures. Any creature that starts its turn in the aura must succeed on a DC 20 Constitution saving throw or take 14 (4d6) poison damage. A creature that succeeds on the save is immune to this sibriex's Contamination for 24 hours.

Can a creature immune to the Contamination ignore the difficult terrain?

Most effects that give immunity after a save that I've encountered (such as a mummy lord's dreadful glare) don't have passive effects outside the save that characters who succeed become immune to.


1 Answer 1



The sibriex's Contamination is a special trait, that is, something listed "after a monster's challenge rating but before any actions or reactions" (MM 10). Everything listed within the Contamination trait (plants withering, difficult terrain, poison damage) is part of that trait.

Note that the trait says "A creature that succeeds on the save is immune to this sibriex's Contamination for 24 hours" rather than saying immunity is granted to the sibriex's poison. Gaining immunity to the named trait through a save means one gains immunity to every aspect of that trait - at least from that particular sibriex.

This is in contrast to other multi-part special traits, where immunity is granted to only a certain part or aspect of the trait. For example, the Gas Spore's Death Burst says (emphasis mine):

The gas spore explodes when it drops to 0 hit points. Each creature within 20 feet of it must succeed on a DC15 Constitution saving throw or [first part] take 10 (3d6) poison damage and [second part] become infected with a disease on a failed save. Creatures immune to the poisoned condition are immune to [second part] this disease.
[Description of disease] Spores invade an infected creature's system, killing the creature in a number of hours equal to 1d12 + the creature's Constitution score, unless the disease is removed. In half that time, the creature becomes poisoned for the rest of the duration. After the creature dies, it sprouts 2d4 Tiny gas spores that grow to full size in 7 days.

Here, note that a creature immune to the poisoned condition is not immune to the entire Death Burst, but just the disease portion of it. That is, a creature that was immune to the poisoned condition would still take 3d6 poison damage on a failed save, it just couldn't be infected by spores. Had the immunity clause said that 'a creature immune to the poisoned condition is immune to the Death Burst', then such a creature would not take the poison damage, either.

Because the sibriex's text says making the save grants immunity to the special trait of Contamination, it grants immunity to every aspect of that trait, including the difficult terrain.

  • \$\begingroup\$ The reader should note that a creature immune to BOTH "poisoned condition" and "poison damage" wouldn't be affected at all by the Gas Spore ability on screen. But Kirt is correct that having only the former doesn't imply the latter even though they might appear together very often. \$\endgroup\$ Commented Feb 26 at 12:59
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    \$\begingroup\$ @MindwinRememberMonica Just so. Cf. Are creatures with the immune to poisoned condition immune to poison damage? \$\endgroup\$
    – Kirt
    Commented Feb 26 at 15:41

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