Effect updates and description changes can be seen here.

Pollutant Gas is a Perseverance deck specific effect card. It deals 1 damage to all enemy monsters on the field, but will deal 3 damage if they are under KR, making Pollutant Gas an all-enemy version of Worsening and the Perseverance version of Patience's Defrosting.

Due to the passive effect of Perseverance, this card will end up giving KR to all enemies, aside cards like Mad Dummy or those with Dodge, such as Sans and Sad Dragon. Because of this, you can combine this with another Pollutant Gas, Contamination, or Asgore.