Freezing sphere

e freezing sphere
Difficulty	9
Attacks	Explode 4d6 cold

e freezing sphere
Difficulty	9
Attacks	Explode 4d6 cold
Base level	6
Base experience	91
Speed	13
Base AC	4
Base MR	0
Alignment	0 (neutral)
Frequency (by normal means)	2 (Quite rare)
Genocidable	Yes
Weight	10
Nutritional value	10
Size	Small
Resistances	cold resistance
Resistances conveyed	cold resistance
A freezing sphere: can fly. does not need to breathe. has no limbs. has no head. is mindless. does not eat. (*) is neither male nor female. is normally generated hostile. can be seen through infravision. does not appear in Gehennom. never leaves a corpse.
Reference	NetHack 5.0.0 - include/monsters.h, line 341

A freezing sphere, e, is a type of monster that appears in NetHack. The freezing sphere is a sphere monster that has an affinity to cold, and it is the only sphere that does not emit light, otherwise behaving mostly like other spheres do.

A freezing sphere has a cold explosion attack that causes them to self-destruct and cover a 3x3 square radius centered on their position, which deals 4-24 base damage to a hero or any other monsters caught in the explosion: this can freeze moats or pools in the explosion's radius and has a chance of shattering potions on the floor and in the inventory of anyone caught in the blast, with the amount of items affected being equal to ¹⁄₅ of the cold damage that was dealt—a hero or monster with a source of extrinsic cold resistance has a ⁹⁹⁄₁₀₀ chance per item of preventing their potions from freezing. Freezing spheres possess cold resistance.

The spellbook of freeze sphere is a deferred feature that teaches a spell the hero can use to create tame freezing spheres.

Killing a freezing sphere with a digestion attack can grant cold resistance to the digesting hero or monster.

Generation

Randomly-generated freezing spheres are always created hostile, and they will not be generated in Gehennom.

A freezing sphere does not leave a corpse upon death.

Strategy

The following information pertains to a recently-released stable version (NetHack 5.0.0) and will be subject to revision as strategy is developed and bugs are discovered and/or fixed.

Explosion attack changes and item destruction refactoring have significant ramifications.

Freezing spheres are fairly annoying to deal with, despite lacking the destructive power of flaming spheres: their movement speed of 13 makes them more likely to catch an unhasted hero, and pets that attack freezing spheres will likely trigger the explosion themselves and catch you or other pets and monsters in the crossfire. While invisibility and displacement can fool a flaming sphere into exploding prematurely, there is a chance the hero may still be caught in the explosion.

If a hero catches sight of a freezing sphere but cannot stash any potions that are on hand, then they may consider dropping them before moving towards the sphere (or else directing it away from that square)—an extrinsic source of cold resistance is among the best forms of protection for a hero's inventory, and dwarvish cloaks can protect items from being burnt ⁹⁄₁₀ of the time, making them viable in a pinch. Freezing spheres can also be lured towards moats, pools and lava in order to make it easier to traverse, though this is somewhat situational: for example, the spheres do not naturally generate in Gehennom, where freezing lava or water makes many of the floors less perilous.

The freezing sphere's nonexistent MR score means they can easily be dropped by poison damage, and they can otherwise be immobilized by means such as a wand of sleep that gives the hero (and/or their pets) a chance to kill them before they explode. Cancellation that hits through their mediocre 4 AC will reliably disable their explosive abilities and render them harmless. Be sure to keep freezing spheres away from leprechaun halls, treasure zoos and similar rooms of monsters that you do not want awakened if possible, and if a zoo contains a freezing sphere, try to save it for last if possible—stealth can be a useful aid for both purposes, though it will not always prevent sleeping monsters from awakening.

History

The freezing sphere first appears in Hack for PDP-11, which is based on Jay Fenlason's Hack, and is included in the initial bestiary for Hack 1.0—the ice ball is a somewhat similar monster included in the bestiary of Hack 1.21, also based on Jay Fenlason's Hack.

From this version to NetHack 3.6.7, including some variants based on those versions, the difficulty of the freezing sphere is 8: its explosion attack targets a single square, has a dexterity-based chance of dealing reduced damage, does not freeze potions, and is completely blocked by cold resistance. Additionally, freezing spheres grant cold resistance only while eaten, which does not account for any form of digestion attack.

The freezing sphere's current behavior is introduced in NetHack 5.0.0 via commit 6b60618e and commit eb22a810, with the explosion behavior adapted from xNetHack, while its monster difficulty rating is increased to 9—NetHack 5.0.0 fixes discrepancies related to the difficulty ratings for spheres via commit c3802343. The ability to gain cold resistance from digesting a freezing sphere is also added in this version via commit 0eadf8df, commit b25961fb and commit c78e7af0.

Variants

NetHack variants created prior to NetHack 5.0.0 may or may not retain the freezing sphere's behavior from previous versions.

SLASH'EM

In SLASH'EM, flaming spheres behave mostly as they do in NetHack 3.4.3 and previous contemporary versions, and additionally have sleep resistance and hit as +2 weapons. As in NetHack, they do not generate in Gehennom.

SLASH'EM makes the spellbook of freeze sphere and its spell functional: casting the spell summons a tame freezing sphere with 1 HP, and casting it at Skilled or higher in matter spells can summon multiple spheres. These freezing spheres will only exist temporarily, and monsters hit by their explosions are treated as though the hero had attacked them, e.g. awarding them experience for monsters that the sphere kills, angering peaceful monsters and so on. The spell also respects extinction, meaning it has a finite number of uses throughout a given game.

All of the above information also applies to SlashTHEM.

dNetHack

In dNetHack, notdNetHack and notnotdNetHack, freezing spheres have an on-death explosion similar to gas spores, covering a 3x3 area centered on it that can freeze potions items in the open inventories of anyone caught in the blast—cold resistance blocks HP damage from the explosion, and extrinsic cold resistance also prevents item damage.

Freezing spheres can be warded by the Elder Elemental Eye at any level of reinforcement.

Freezing spheres may be generated in the Lawful Quest, where they will appear on the Paths of Law and within the Arcadian Tower if Oona's elemental affinity is cold. The summon sphere monster spell can summon freezing spheres.

SpliceHack

In SpliceHack, freezing spheres behave as they do in NetHack 3.6.7 and previous versions.

The spellbook of freeze sphere is made functional and works similar to SLASH'EM.

Reading a scroll of elementalism while confused has a ¹⁄₄ chance of summoning freezing spheres, which are tame if the scroll was blessed and read by a hero and will otherwise be hostile.

All of the above information also applies to Hack'EM.

EvilHack

In EvilHack, freezing spheres use explosion attacks and on-death explosions that cover a 3x3 radius centered on its square, freezing monsters and potions caught in the explosion.

Encyclopedia entry

See the encyclopedia entry for sphere.