Potion of Diminution
Potion,
Rare
(cost 550 gp)
Crafting Components
Gilded acorn, sapphire, vial of primordial vitae
A golden acorn floats in the translucent liquid, dropping from the top of the vial and floating back up every few seconds. After drinking this potion, your size is reduced by half (as the enlarge/reduce spell but without need for concentration ) for 1d4 hours.
Source