Poison Cloud is a level 65 Elementor AoE. It has the Water element. Its animation is a large cloud forming and raining down green liquid, with circles radiating outwards below like ripples. This does damage over time, such as 100 every 5 seconds.
This skill is almost universally considered to be underpowered.
It can be very useful for a Hit and run Elementor if they alternate it with another aoe spell (such as the Windfield).