Rhyolite wastelands: a very flat, and lifeless biome. It is made primarily out of rhyolite, a smooth, tanish rock with gray bits. Located in this biome is a new ore (kind of), rhyolite quartz ore. This is because rhyolite is partially made of quartz. Rhyolite quartz is just like regular quartz ore, but it looks like rhyolite instead of netherrack. You can use rhyolite to make rhyolite tools, which are about as good as wood. There is probably some kind of structure that would spawn in this biome. That was a long idea. :)

charred forest.
it has wood that deosnt burn (even when the item is in lava like netherite)
and the wood is black in colour.
it has ambient noises like the basalt deltas, and the terrain is a rougher version of the crimson forest.
mobs that would spawn include piglins (in groups of 2 with 1 brute as the leader) and hoglins also spawn (rarely).
nether gold is common as well as magma cubes.
netherite is found here more commonly then in other biomes.
wither skeletons spawn here as well
there is very little glowstone, fire or lava to keep it dark.
there is a thick fog as well

Ashen Spikes Biome

like ice spikes but for the nether, would have new blocks called Ashstone and there would be a rare ore called Ash Steel

put a cool nether mob

Volcano

And in the volcano is a stronghold guarded by piglins (not just the ones in-game, but other kinds like the ones in MCD), essentially a larger and upgraded bastion

Make a cold/icy biome in this dimension, some sort of drip stone cave but frozen and with stalactites, and a new hostile mob

An over world biome in the nether that is super lush, but has over world villagers that are protected by very strong guards. The villagers are overpowered variants of the over world ones, so they are worth fighting the guards.

make a upside down biome, a normal barren wasteland or smth but the terrain is upside down and you have to get to the top to collect more resources and stuff

the mod will be for 1.19