One mixin mod that makes all structures (including non-vanilla ones) more spread out (essentially making them rarer). Useful for big modpacks with lots of structure mods to make exploration more challenging/less repetitive.
Sky Archipelago adds a new floating-islands world generation. High degree of configurability, such as island density, sizes, Y-spawn heights, ocean or void and much much more!
A highly configurable overhaul of Minecraft's way of progressing through the game : bosses, RPG-like, new mechanics, multiplayer compatibility, weapons, ores... !
A mod that adds a malevolent god and a wrathful cult back into your world. Focused on practical use, something that you can add without being interrupted constantly.