D&D 5th: Demon Tower of Madness
Potion of Diminution
Property [Consumable]: Potions/Oils are consumable magic items. At minimum, drinking or applying a potion requires an action, consuming the entire potion. Similarly, administering a potion to someone else requires an action. Once used, a potion takes effect immediately, according to its effect.
After drinking this potion, the individual (and everything he’s carrying and wearing) diminishes in size—to as small as 5% of normal size. The percentage of the potion drunk determines the amount a character shrinks: For example, if 40% of the contents are swallowed, the person shrinks to 60% of normal size. The effects of this potion last for six turns plus 1d4+1 turns.