Caustic's Independent Variable

When you cast this spell, you add an independent variable to an empty space you can see. The variable is a small canister, and does not occupy the space. The variable is compact and requires a successful Wisdom (Perception) check against your spell save DC to be found. Any creature who sees the spell being cast may make this check once with no action required. This check must be made at disadvantage if the variable is placed in difficult terrain.

The variable is triggered when a hostile creature enters within five feet of the variable or ends their turn there. When triggered, a poison cloud with a radius of 20 feet appears, and all creatures within the area must make a Constitution saving throw. On a failed saving throw, they take 2d8 poison damage and are poisoned while they remain within the cloud. Vision is heavily obscured for all creatures within the cloud. Each creature within the area takes 1d8 poison damage at the start of their turn, and their speed is reduced by half.

You can hit the variable with an attack to trigger it as well. The variable has an AC of 12, and 1 hit point. An enemy who has detected the canister can destroy it by attacking a specific part of it - When targeted this way, the variable has an AC of 18 and 1 hit point. If this attack roll misses by 5 or more, the attack roll triggers the variable instead.

The poison cloud lasts for 1 minute, and can be dispersed by a strong wind.

At Higher Levels. When you cast this spell using a spell slot of 4th level or higher, the initial damage of the poison cloud increases by 1d8 for each level above 3rd level, and the AC to destroy the variable increases by 1.