Diminution

Diminution: This potion reduces the drinker and all items worn or carried to one-twelfth of their original height (so that a 6' tall character becomes 6" tall). The drinker's weight is divided by 1,728; this makes an armed warrior weigh less than 2.5 ounces. The affected creature cannot make an effective attack against any creature bigger than a house cat, but may be able to slip under doors or into cracks and has a 90% chance of moving about undetected (both in terms of sound and vision).