Custom 100-Day BOSS

Custom 100-Day BOSS generates biological entities on a schedule. Every 100 days by default, a boss spawns, and the entity list is set by registry names such as minecraft:zombie or minecraft:creeper. Bosses appear one after another in the order given in the list, so the sequence is predictable once it is configured. Players change the settings in the config file found in the config folder of the game directory. Days between boss spawns can be set from a minimum of 5 up to the default of 100, and a switch turns the boss spawn feature on or off. Spawning can also be toggled in game with commands when the server owner allows it, using 100dayboss true to enable and 100dayboss false to disable.

Bosses are placed in safe zones, which are open spaces without obstructions, so a creature does not end up stuck inside blocks. Spawns can take place in other dimensions, and the mod works alongside dimensions added by other mods. In most dimensions a safe zone cannot be located three blocks above the player, so placement there follows the terrain rules instead. The mod is published for Forge and NeoForge, with files for four game versions: 1.18.2, 1.19.2, 1.20.1 and 1.21.1. The latest files are 1.4.0 for 1.20.1 on Forge and 1.4.0 for 1.21.1 on NeoForge, both dated 2025-06-25. Only the client needs the mod, and it is released under the MIT License, though it is not open source.