Mysterious force

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In NetHack, the mysterious force is a feature that occurs in various places:

  • Non-teleport levels will print the message "A mysterious force prevents <foo> from teleporting!" any time you or a monster attempts to teleport on that level.[1]
  • Another "mysterious force" prevents you from descending the staircase on the quest home level without first getting permission from your quest leader.[2]
  • While digging with a blessed pick-axe on the Plane of Earth, a "mysterious force" may create a cave around you.[3]
  • If you are being escorted out of a vault and drop the gold on a square where the vault's walls used to be, a "mysterious force" will move it back into the vault when the walls are magically repaired.[4]

This article describes the most relevant instance of the mysterious force for most players: a random level teleportation effect that occurs while carrying the Amulet of Yendor in Gehennom. It is mostly known as the much-maligned primary obstacle that you face during the ascension run.

Description

When trying to climb up stairs or quaffing a cursed potion of gain level in Gehennom with the Amulet of Yendor in your possession, the mysterious force will activate 14 of the time and impede your progress.[5] The mysterious force does not act when you go up from the Valley of the Dead to the Castle, or when you enter Vlad's tower using the staircase. If you are inside the Wizard's Tower, it will leave you on the same level if it would otherwise place you below the bottom of the tower.

The mysterious force will often push you back by at least one floor; it can also teleport you around the same level as a kind of "zero level drop". You may also be sent back more than one floor depending on your alignment: Lawful characters are dumped up to three levels below their current location, while neutral players are dropped up to two floors below, and chaotic characters are the most fortunate, with a maximum of one level down.

Monsters, especially the Wizard of Yendor, may also be affected by the force when they try to flee upstairs with the Amulet. Unlike the player, monsters that are not already in the three lowest levels of Gehennom will always be sent exactly one level down by the force, and will be placed near the up staircase.[6] Cursed potions of gain level will also not trigger the mysterious force for monsters. These effects are summarized in the table below:

Level change Lawful Neutral Chaotic Monsters
​−1 75.00% 75.00% 75.00% 75.00%
0 6.25% 8.33% 12.50% 0
+1 11.45% 12.50% 12.50% 25.00%
+2 5.20% 4.17% 0 0
+3 2.08% 0 0 0
Avg. Change -0.470 -0.542 -0.625 -0.5

Strategy

Since Gehennom also contains many non-teleport levels, the player is advised to save a few cursed potions of gain level to bypass especially convoluted levels, such as Asmodeus' Lair. The annoyance that the mysterious force causes is enough for some to bring along or wish for a helm of opposite alignment in order to temporarily convert to chaotic alignment and avoid the worst of it, especially during speed ascensions using dwarven Valkyries.

There os an advanced strategy to bypass a few levels in the lower sections of Gehennom by taking the portal to the Wizard's Tower, which typically moves you a few levels upwards (note that the force is less harsh inside the Tower). The strategy involves stoning the Wizard of Yendor when you first encounter him to obtain the Book of the Dead, which as a unique item will not be trapped within his statue - you then return to the Tower during the run to the surface, unstone him and toss him the Amulet. You can then escape the level via levelporting and meet the Wizard on the upstairs, and he should teleport to you with the Amulet.

Probabilities

The following information pertains to an upcoming version (NetHack 3.7.0). If this version is now released, please verify that it is still accurate, then update the page to incorporate this information.

The force has been changed to hit you less often proportional to the total number of levels you have been sent back already. Most of the calculations on this page will be invalidated.

The following values are for a typical 22-level Gehennom. On average, Lawfuls take around 30% longer than Chaotics, and Neutrals take around 14% longer. Before the corrected probabilities were discovered, players used to believe that Lawfuls had a much harsher penalty when escaping Gehennom.

Lawful Neutral Chaotic
Average staircase climbs (approx) 45.2 39.8 34.9
Climbs for 90% chance of escape 63 53 43

History

Despite a code comment in NetHack 3.4.3 implying that the probabilities of each distance other than -1 are equal, this is not actually the case - the code actually randomizes the distance to move a player twice, leading to the above distribution in the first table. Later versions of NetHack would change the comments to describe the formula correctly.

Messages

A mysterious force momentarily surrounds you...
You were affected by the mysterious force and did not move up a level.
As <monster> climbs the stairs, a mysterious force momentarily surrounds <him>...
A monster carrying the amulet was affected by the force and moved to the previous level.

Variants

SLASH'EM, SporkHack, UnNetHack, xNetHack, EvilHack and SpliceHack have completely removed the mysterious force. UnNetHack, xNetHack, EvilHack, and SpliceHack compensate for this by making carrying the Amulet block all teleportation, including intra-level.

UnNetHack and EvilHack also include an effect that can make the Amulet of Yendor teleport itself to a random location on the current level whenever it is dropped for any reason. The odds of it teleporting away depends on its BUC status.

References

This page may need to be updated for the current version of NetHack.

It may contain text specific to NetHack 3.6.1. Information on this page may be out of date.

Editors: After reviewing this page and making necessary edits, please change the {{nethack-361}} tag to the current version's tag or {{noversion}} as appropriate.