You conjure a lightly coloured and corrosive cloud of vapour in an area.

The cloud spreads around corners and lingers in the air for the duration. The area is considered Lightly Obscured, imposing Disadvantage on WIS (Perception) checks in that area. The cloud is dispersed when it interacts with wind of moderate or greater speed (at least 30kmh^-1).

When a creature begins its turn in the cloud or enters the cloud for the first time on a turn, it makes a Constitution saving throw, taking 1d12 Acid damage and receiving stacks of

Sap

Critical Success (+10). The target is unaffected.
Success. The target takes half damage and receives 2 stacks of Sap.
Failure. The target takes full damage and receives 4 stacks of Sap.
Critical Failure (–10). The target takes 1.5× damage, and receives 6 stacks of Sap.

Either way, any nonmagickal metal armour or metal shields that they are wearing takes a permanent and cumulative –1 penalty to the AC it offers. Armour reduced to an AC of 10 or a shield that drops to a +0 bonus is destroyed. Also, any nonmagickal metal weapons that they are wielding take a permanent and cumulative –1 penalty to attack rolls and damage rolls. If its penalty drops to –5, the weapon is destroyed.

Objects that are vulnerable to corrosion that aren't being worn or carried automatically corrode if they are in the area.