It adds an insane list of minerals, enough to make a survival world underground with only a pickaxe and finish by beating the ender dragon, without even going to the surface once. Also, Redstone, lapis and emerald tools and armour.
It's a mod that adds lots of stuff, most importantly ores
Adds many references to the Bfdi universe, as well as other stuff
Adds a block that can duplicate items and other blocks