Edit: These poison is intentionally designed not to disappear over time. I'm sorry for the misunderstanding.
Below is the original feedback:
In map 4, some poison created by some monster attacks will persist until the end of the fight in the room, and will not disappear over time like other poison created by monsters.
Attacks that have been found to create such non-disappearing poison include: spit attack of Snortoise and elite Snortoise, slam attack of elite Snortoise, kick attack of elite Floracrane and Greater Floracrane.
The color of such non-disappearing poison is different from the other poison created by the monsters, and is similar to the poison originally present on the ground.
The maximum amount of such non-disappearing poison seems to be 11 pools, poison created by the aforementioned attacks will disappear over time from the 12th pool and become similar in color to other poison created by monsters.
By the way, the poison which introduced in map 4 is called "Acid" in Market Challenge while called "Poison" in other texts, is this a name inconsistency problem?
Let Snortoise, elite Snortoise, elite Floracrane or Greater Floracrane to perform the aforementioned attacks.