Monster with gas attack that eliminates immunity to poison?

[ksbsnowowl]

Being in Kansas City, with our dump of 16" of snow and ice in ~12 hours, my last two days have been spent at home working on lots of D&D preps for my campaign.  I came across a monster that I now cannot remember, and it had an ability that was some sort of cloud it released that made foes more susceptible to poisons, even removing immunity to poison, if I recall this thing correctly.

Any idea what this creature is?

[Scottzar]

Poisoner’s Breath (Su) Sertrous’s breath fills a 240-foot-radius
spread around him. Any creature that breathes this
foul air must succeed on a DC 33 Fortitude save or be
sickened for 1 round. This breath suppresses any immunity
to poison a victim possesses for as long as it remains
within the area plus an additional 2d6 rounds after it
leaves the area.

Elder Evils, page 115 - 116

I assume this is what you remember.

[ksbsnowowl]

That was it.  Thank you!