Blue jelly

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A blue jelly, j, is a type of monster that appears in NetHack. Like most jellies, it is eyeless, amorphous, and sessile.

A blue jelly has a passive attack that triggers if attacked in melee, dealing cold damage against attackers without cold resistance dependent on their level while increasing the jelly's HP by half the damage inflicted[1][2][3][4] - if enough HP is gained from this, the jelly will undergo division, halving its HP (rounded up) and creating a second jelly with almost the same amount of HP.[5][6][7] Blue jellies possess poison resistance and cold resistance.

Eating a blue jelly corpse or tin has roughly a 215 chance each (13%) of conferring cold resistance or poison resistance.


Randomly generated blue jellies are always created hostile.

Blue jellies appear among the j that make up the second quest monster class for Knights, and makes up 6175 of the monsters that are randomly generated on the Knight quest.


Avoid attacking a blue jelly in melee unless you have cold resistance: blue jellies are much tougher than might be expected, and their cold passive attack can be deadly to inexperienced players. At their base level, they do (4+1)d6 damage, which gives a range of 5–30, and they can be generated at much higher levels. Ranged attacks are preferable, but make sure you have enough charges or projectiles options to finish the job—projectiles in particular will not be retrievable until the jelly is dead.

A lance or polearm can pound away safely at a distance and take one out easily. The aklys is a solid option for throwable weapons that should likely be prioritized below pounding, but above other thrown weapons other: at worst, the aklys has a 1100 chance of failing to return, but will most likely deal enough damage for a character to finish it with any remaining projectiles, preserving valuable darts, wand charges and/or other items. Sources of fire damage can also make short work of blue jellies.

Blue jellies are frequently employed for boulder forts, stashes, and the like since they are completely immobile.


The blue jelly first appears in NetHack 3.0.0.

In NetHack 3.4.3 and earlier versions, including some variants based on those versions, blue jellies can be instrumental in farming the Rider Death.



In UnNetHack, a blue jelly appears in one of the corner rooms of Asmodeus' Lair.


In SpliceHack, a blue jelly appears in one of the corner rooms of Asmodeus' Lair as in UnNetHack.


In EvilHack, blue jellies are vulnerable to fire. This also applies to Hack'EM.

Encyclopedia entry

I'd planned how to prevent the lock from sealing behind me; it required a temporary sacrifice, not cleverness. I used the door itself to help me cut off a portion of my body, after shunting all memory from the piece to be abandoned. The piece, looking inexpressibly dear and forlorn for a bit of blue jelly, would force open the outer door until I returned and rejoined it.

[ Beholder's Eye, by Julie E. Czerneda ]


  1. src/uhitm.c in NetHack 3.6.7, line 2917: case for cold passive against you
  2. src/uhitm.c in NetHack 3.6.7, line 2917: cold passive healing against you
  3. src/mhitm.c in NetHack 3.6.7, line 1671: case for cold passive against monsters
  4. src/mhitm.c in NetHack 3.6.7, line 1682: cold passive healing against monsters
  5. src/uhitm.c in NetHack 3.6.7, line 2933: case against you calls split_mon function in potion.c
  6. src/mhitm.c in NetHack 3.6.7, line 1685: case against monsters also calls split_mon function in potion.c
  7. src/potion.c in NetHack 3.6.7, line 2379