Nightcore currently adds four new mobs and three new structuress: the Barbarian, Zombie Cow, Zombie Pig and Zombie Sheep. The Barbarian has decent AI and will collect logs and stone, and with the gathered materials it will build structures and make weapons. Barbarians are about as fast as the player and will tear through leaves with ease. They also attempt summon a new barbarian every night. Zombie animals spawn one hour after killing the same type of animal, and helps encourage people not to build huge cruel animal farms. The new structures include two types of Barbarian Camps, as well as the Spider Temple (found above ground.)
Future update Ideas:
Better Barbarian Texture: Self explanatory
Better Barbarian AI: Build a larger variety of structures, collect materials more slowly
Corrupted Mobs: The Longer you survive in the world, the more corrupted the world gets. For example, after 30 days, corrupted start spawning very rarely. After day 200 they would be common. After you kill the Ender Dragon the corrupted would disappear. They wouldn't have any special drops.