Valentias Entropy

The mod is focused on expanding the progression of the main game. It adds a large amount of content with a whole new progression path, built around unique materials and mechanics. New mobs, new materials and ores, and new crafting tables give the progression its structure, and several ore tiers lead to weapons that players use throughout the world.

Most of the additions are meant to be reached through the normal vanilla world, so the content continues past the Ender Dragon. World generation was changed to avoid conflicts: the deepslate layers between Y-42 and Y-64 are replaced by a new stone called Core Stone. The author notes that this can still cause issues with other mods that generate ore, and that the mod can cause some lag while the world first generates.

Valentias Entropy is published for Forge and for 1.20.1 only, under All rights reserved, so it is not open source. Client and server both need the mod, so every player on a server that runs it has to install it too.