Vampire Forest
From Feed The Beast Wiki
The vampire forest is a rare to find biome,where grows an unique plant that can be used to trade with expert vampire villagers,and the home of lords,depending on the level of an close player,the level of an lord,is decided by that,if you have max level,there will be more chances of a level 5 lords spawn,another characteristic of the biome,is that vampires are safe from sun while they are inside the biome.