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Nucleepers are rare hostile mobs found in the the Toxic Caves. They are larger and slower Creepers that take longer to prime themselves for detonation, but cannot be interrupted once they start charging up and create a devastating nuclear explosion if allowed to finish.

Cave Compendium Entry

"The Nucleeper is some form of highly modified creeper with mechanical and atomic enhancements. This poor creature seems to be in a state of constant anguish, just like its normal creeper ancestors. Nucleepers are slow, and take much longer to charge up their explosive ability than normal creepers. This begins with the core of the creeper beginning to close, emitting a warning siren sound and bright flashing lights from its glowing green head. Once the core of the creeper has completely closed, an atomic explosion will appear and devastate the nearby area. For this reason, Nucleepers must be destroyed before they close completely and create an atomic fireball. If slain before it reaches criticality, it can drop some gunpowder and occasionally a Fissile Core..."

- Dr. Prof. Alexander Caverns, PhD.


Nucleepers can spawn anywhere in the Toxic Caves under normal monster spawn conditions.


On death

Item Roll Chance Quantity (Default) Quantity (Looting I) Quantity (Looting II) Quantity (Looting III)
Fissile core.png Fissile Core 100% 0-1 0-2 0-3 0-4
Gunpowder.png Gunpowder 100% 0-2 0-3 0-4 0-5
Grid Fusion Disc Fragment.png Fusion Disc Fragment 100% [1] 1 1 1 1
  1. Only dropped when killed by a Tremorzilla's energy beam.


Nucleepers act similarly to standard Creepers, chasing players within a 16-block radius and leaving other mobs alone unless provoked - they can step up one full block without having to jump. Once they get within 3.5 blocks of their target, they will begin to charge up, causing the plates around their head to close up while radiating 2 rays of green light that spin around increasingly fast and emitting a whirring noise punctuated by beeps that gradually intensify, in addition to activating any Nuclear Sirens in a 256-block radius and causing any mobs that provoked them to start targeting them; once they initiate their charge-up, they will continue even if their target moves more than 4 blocks away from it, usually only stopping upon death. Should they fully charge up, their bodies will flash a bright green and distort before creating a powerful nuclear explosion that has a blast radius of 25 blocks and spreads fires, causing the screen to flash white and briefly muffling all audio upon exploding - in addition to the initial blast, they will emit a field of nuclear energy that spreads across a 37.5-block radius, dealing 2 HP of damage every 0.2 seconds to any players and mobs caught in it in addition to inflicting Irradiated II on them for 40 minutes.

A Nucleeper's explosion leaves a crater 25 blocks wide and 8 blocks deep. If /gamerule mobGriefing is false, then it will not leave a crater at all.

Similarly to standard Creepers, Nucleepers can be ignited with flint and steel or fire charges, immediately starting their charge-up.

Unlike standard Creepers, Nucleepers are not silent - they will beep and hum when idle, in addition to making quiet clanking noises as they walk. This allows a player to detect a Nucleeper easier as it approaches them.

Nucleepers will flee from any Raycats within a 10-block radius. Nucleepers that are fleeing from Raycats will be unable to charge up until they get far enough - if they initiated their charge-up beforehand, they will reverse it, completely stopping should they fully reverse.

Resistances and weaknesses

As inhabitants of the Toxic Caves, Nucleepers are unaffected by the Irradiated status effect, in addition to being immune to acid.

Due to their cybernetic nature, Nucleepers are greatly affected by nearby neodymium blocks, similarly to players wearing iron or Netherite armor, Iron Golems, and minecarts.


1.0.0 Introduced.
1.0.4 Now respects the mobGriefing gamerule.
1.1.0 Now drops a Fusion Disc Fragment when killed by a Tremorzilla's energy beam.


  • Similarly to Guardians, Nucleepers will follow players with their eyes rather than turning their heads to stare at them like most other mobs.
  • Nucleepers use similar hurt and death sounds to standard Creepers, albeit pitched down and underlaid with metallic clanging.
  • Nucleepers have a default charge-up time of 15 seconds. This charge-up time can be altered in the general config file, with 1 full second being the minimum amount of time that can be entered.