It adds a new feature, every-once and a while, you will find a vast cut in the earths crust and have to build a bridge to cross. If you're lucky a mineshaft will do it for you. There will be no updates for this mod. If you have trouble, it's you not me. Does not require mod-loader. And as with most biome adding mods, it will make a casual gamer's computer quite laggy. Please ask permission before uploading maps to pmc. I will never say no.
Good for houses, ores, spelunking, general adventure, challenge maps. Blah, blah, blah.
Just play it. Slimes do not spawn in this biome.