Youll encounter many hazards while exploring Thymesia's ruined world, such as corrupted foes, and an unsettling yellow fog. This fog will slowly poison you over time, and can kill you very quickly if you havent put much effort into it.
How do you clear the yellow fog?
To remove the yellow fog from an area, you must destroy the large pulsing yellow pustule that should be nearby. You can use melee attacks or ranged feather attacks to cause less damage from a distance, but you'll likely be poisoned quite rapidly. It's usually better to grab a ladder or climb up an obstacle course quickly rather than trying to remove the yellow pustule.
The yellow pustule forms early in the game, and there's nothing you can do about it. In most areas, there will be a quick exit that you can reach somewhere in the fog, usually a ladder. It's better to go to these and progress than it's to remove the yellow fog. In some situations, the pustule will be hidden on another level above or below you, so you may need to climb a ladder or ladder to exit the area.