You see what seems to be a miniature tree within this glass vial.  If throwing this potion, make a ranged weapon attack.  The creature that consumes this potion, or has it applied to comes under the effect of the barkskin spell.  Their skin turns to a dark brown color, with a rough firm texture, like the bark of a tree.  Regardless of what armor the character is wearing, their AC is counted as 16.  The duration lasts for 1 minute.

Notes: Set: Armor Class