ChallengeX

Players set up a challenge by combining pieces: a rule, a modifier, a trigger and a win effect. Each piece is optional, so a run can use one rule or several, and a builder can stack many. The mod ships its building blocks with 19 modifiers, and a composed challenge can be exported as a preset file or shared by link. The builder runs entirely in the browser, so nothing needs to be installed to try it.

A run has a clock on the action bar that counts up or down against a time limit, and it can be paused or resumed, freezing the world, mobs and clock for everyone. Players who drop out enter spectator mode, and when a run finishes the mod reports where each player was placed and how long the run took. Progress persists between sessions for each world. A challenge can also be set to target specific players, for example making one player permanently blind while another is barred from jumping.

Installation depends on the server type. On Fabric, Fabric API is required, and the ChallengeX build goes into the mods folder. On Paper, the ChallengeX build goes into the server's plugins folder. The Fabric mod and the Paper plugin differ only in the shared-inventory modifier, which is Fabric-only. ChallengeX is server-side only, so vanilla clients join with nothing extra. The mod is published for 26.2 and 26.3, and it is released under the Creative Commons Attribution Non Commercial Share Alike 4.0 license, so it is not open source.