Hello @Shinoow with latest version of Abyssalcraft(1.7.8.1) biomes of AC are generated on the nether. Can you solve this problem, please? Thanks again for your work, this mod is fantastic!

That might be a biome ID conflict with Biomes O' Plenty, as that mod generates new biomes in the nether.

Yes, all biome are overwrited, I fix manually. Thanks for tell me this @Shinoow .

With this:
biomes {
I:"Abyssal Wasteland"=169
I:"Coralium Infested Ocean"=179
I:"Coralium Infested Swamp"=178
I:"Dark Realm"=181
I:Darklands=168
I:"Darklands Forest"=174
I:"Darklands Highland"=176
I:"Darklands Mountains"=177
I:"Darklands Plains"=175
I:Dreadlands=170
I:"Dreadlands Forest"=172
I:"Dreadlands Mountains"=173
I:Omothol=180
I:"Purified Dreadlands"=171
}

Id shouldn't be overwritten.