Citadel

Citadel is a library mod created by AlexModGuy. A modding library required by Alex's Mobs and Ice and Fire providing animation systems, entity utilities, and data tools. As a library mod it concentrates on shared code that other mods build on, and it has been downloaded around 70 million times, which puts it among the options players reach for in this space.

Citadel is built for players installing Alex's Mobs or Ice and Fire, which require it. Citadel is the library powering those creature mods' animations and systems, installed alongside them as a dependency. It is approachable enough to drop into a world and use right away, with little setup required.

The mod is available for Forge and NeoForge, so it fits a range of modpacks and launchers. It currently supports Minecraft 1.20.1 and 1.21.1, spanning the 1.20.1 to 1.21.1 releases. It runs on both the client and the server, so on a multiplayer server every player who connects needs it installed alongside the server itself.

Citadel works particularly well alongside Alex's Mobs and Ice and Fire: Dragons. It targets the Forge side of the ecosystem, so it fits comfortably into Forge and NeoForge packs.

As a library mod, Citadel adds no content of its own and has a negligible footprint, it exists to support the mods that depend on it.

If you are comparing options, a similar mod worth a look is (no direct alternative, it is a dependency library). They overlap in purpose, so most players pick whichever suits their loader and pack.