Hydrological by Apothicon is a worldgen mod that overhauls the overworld by reworking vanilla biomes and adding unique terrain in fantasy-style. It is in beta and some vanilla biomes are not yet implemented while non default world presets may not work.
Ore generation is custom and unusual, with copper and gold veins on dripstone cave walls, iron and coal veins on lush cave walls, redstone spikes in lava aquifers, diamond and magma shafts above bedrock in non Deep Dark caves, and lapis and packed ice shafts above bedrock in Deep Dark caves. Dozens of new tree types are added and they are generated so they do not clip into nearby trees, which makes deforestation cleaner, and all of them can be grown from saplings with instructions shown in the item tooltip. There are new world presets like Floating Islands and Floating Caves that work on Neoforge and 1.21 plus.
Other features include fireflies that spawn at night around tall grass, vanilla like custom blocks such as leaf piles and wood walls which are toggleable, a few blocks that emit light like blue ice, and custom temperature based fog that can be toggled.
Download now: https://www.curseforge.com/minecraft/mc-mods/hydrological
