SCP-2521, ●●|●●●●●|●●|●

The mob is the central piece of the mod. A black figure appears in the world when a player writes the number 2521 in chat, or in a book named 2521, and the figure carries its own number that is written and spoken. Most mobs in the mod use special spawning conditions, so they appear only when certain requirements are met. Some spawn only above Y level 60, some only below it, and most only in the Overworld rather than in other dimensions. Spawning conditions are checked in order, and the mod does not change how vanilla spawning works for other mobs.

The mod requires Geckolib, which must be installed alongside it. Installation covers the server and each player's game. Files are published for Forge only, for 1.19.2 – 1.20.1 across three release versions, with 1.0.0 for 1.20.1 as the latest file. The mod was made with MCreator and includes a config file. The author notes that the newest game versions are recommended, because version 1.19.2 lacks some features present in 1.20.1. Signs and books are unaffected by SCP-2521 due to MCreator limitations, and the author tried to add a further mechanic without success. Only the chat function works fully.