With version 1.3 of nether x, nether biomes have been added to the nether! The normal nether biome is still the most common, but there are also three other biomes added as well! They will work with the biomesOPlenty nether biomes also, so you can have all the nether biomes you could ever want!
Normal nether biome - the main nether biome is still the most common one found in the nether. It is still mostly like the vanilla nether but with a few changes. The first one is that the vilewood trees are found throughout it. Another change is that there are poison ponds, (similar to overworld water ponds). The third thing added is the ores that are found around. They are ichorite, venomite, necromite, and magma. There may be more in the future.
The Mushroom Swamp - a biome filled with mushrooms, oozing poison lakes, fungal strands, giant mushrooms, and the occasional vilewood tree. Magma cubes spawn much more frequently here. Witches may spawn here in a later version of Nether X, but are not currently added.
The Soul sand Desert - an ancient biome filled with vast amounts of soul sand, Inferno spiders, and cursed soul sand which works like quicksand in the nether. The soulsand desert is a difficult biome to explore because of all of the soul sand slowing you down while mobs try to attack you. A helpful thing to have here is a swiftness potion so you can move faster.
The Spiked Caverns - a lame name for a really cool biome. Filled with towering stalactites and stalagmites, islands jutting out of the lava ocean, and frequent lavafalls, this biome is a great place to build a fortress in.
If you don't for some reason like the Nether biomes, you can easily disable them in the config.