Potion of gain level
|Base price||300 zm|
|Monster use||May be used by monsters as misc items.|
Quaffing a non-cursed potion of gain level will increase your experience level by one. An uncursed potion will set your experience points to the minimum for your new experience level, while a blessed potion will set your experience points to a random value from the minimum to the maximum for your new experience level. For example, if your experience level is 2, quaffing an uncursed potion will increase your level to 3 and set your experience points to 40 (the minimum for level 3), while quaffing a blessed potion will set your experience points to a random number from 40 to 79 (80 points is the minimum for level 4).
When you gain a level, you get increased maximum hit points and energy, the amount depending on your level, race, role, and constitution. If you are already at the maximum level (30), a non-cursed potion of gain level will still increase your HP and energy.
A cursed potion does not increase your experience level, but does affect your dungeon level as one of the game's many puns; quaffing one "decreases" it by one, causing you to rise through the ceiling to the floor above. However, this does not work in any of the following locations: the End Game, Sokoban, the top floors of the Wizard's Tower and Vlad's Tower, the top floor of the Quest, and Fort Ludios. They also do not work on dungeon level 1, unless you are carrying the Amulet of Yendor. Quaffing the cursed potion in these places will only give you an "uneasy feeling."
Use by monsters
An intelligent monster with hands will quaff a potion of gain level if it finds one, or if it is generated with one in inventory. If the potion is not cursed, the monster will gain experience, and possibly grow up into a more powerful version (e.g. a master lich into an arch-lich). If their grown up form is genocided, the monster will die. If the potion is cursed, the monster will rise through the ceiling unless they are in one of the aforementioned locations; in those cases, the monster "looks uneasy". Only witnessing a monster gain experience will auto-identify the potion, though witnessing the cursed potion's effects will prompt you to name it.
If attempting to gain experience levels, blessing potions of gain level before drinking them makes more sense earlier in the game than later. At higher levels, usually around the time you are quest-ready (e.g. XL 14-17), the number of experience points needed to level up through normal adventuring runs into the hundreds of thousands, such that there is little point in blessing a potion before quaffing; potions, foocubi, and wraith corpses are the most viable methods available at that juncture.
Cursed potions of gain level are most useful for quickly leaving Moloch's Sanctum and other non-teleport levels while on the ascent to the Elemental Planes, and can be used as an escape item in a pinch.
For alchemy, potions of gain level have the same uses as potions of gain energy. This is sometimes useful if you have potions of gain level to spare, but gaining an extra level of experience is generally a better idea. There is also an alchemy recipe for producing them, and by extension a multiple-step alchemy recipe.
In SLASH'EM, items dipped into a potion of gain level are upgraded, much like using the gnomish tinker technique. This does not violate polypileless conduct. This can be used to identify potions of gain level: if you dip an upgradable object into a potion and receive the message "Hmm! You don't recall dipping that into the potion," then you will be prompted to name the potion. The potion of polymorph will also change the item, but does not produce this message and auto-identifies.
The potion is also more worth quaffing (and thus blessing) in SLASH'EM, as the lower XP requirements for gaining levels make it feasible to advance a level by killing enough monsters for a longer period in comparison to vanilla.