- ""I Missed Christmas Vacation thanks to that Poltergeist; had to stay in the hospital wing; quite miserable being that helpless and not being able to do anything for yourself."
- ―Oliver Lestrange referring to Peeves force feeding him a Regression Potion
Unlike most potions, the Regression Potion’s base liquid is cow’s milk. To brew the potion, you add 1 gallon of cow’s milk to a cauldron, then wait for it to start boiling. Once it does so, add 5 ounces of crushed premature mandrake root. Let that boil for 20 more minutes, then add 3 ounces of powdered fairy wings to the potion before 21 minutes of boiling passes. Let the potion then stew for 1 month, then add a hair of a newborn unicorn that was less than 1 minute old when the hair was clipped off to the mix. After this is done, stir the potion counter-clockwise 7 times and let it boil for 10 more minutes. The potion will then be complete, and around 30 ounces are available of the potion after brewing.
This section states what happens when you mess up the brewing instructions in a certain way. Any other mishaps while making the potion will simply render it useless.
- If you add more than 5 ounces of crushed premature mandrake root, then the potion will cause you to become one year younger each day after the initial drinking until the 30 days end. If this de-ageing would put the drinker below a physical week old, it will instead act as if the drinker drank too much of the potion, thus keeping them physically a week old and having them age at a normal rate. This can also stack with the mishap involving the powdered fairy wings.
- If you add less than 3 ounces of powdered fairy wings, the drinker will also lose their memories and behaviors up to wherever they are physically aged. These memories and behaviors are regained once the drinker reverts to their normal physical age, as well as any memories gained while regressed. However, this effect can stack with the mishap of the crushed premature mandrake root and drinking too much of the potion, so it is possible to keep losing more memories and behaviors each day, and even have a permanent effect.
- If you stir it counter-clockwise more than 7 times, or stir it clockwise once, the potion evaporates into a pink cloud, and anyone within the pink cloud has their physical age reverted to 1 month old. The normal rules for ending the potion apply for this effect.