Herobrine is one of those characters in Minecraft who tend to never fade (even though he doesn't exist in the original Minecraft - sorry to disappoint you!). In this mod you can bring Herobrine to life. Though, he's no nice guy it appears like as he wants to kill you.
He's no easy kill so make sure you wear your best armor. Preferably a diamond armor.
What can Herobrine do? In this mod, as we've mentioned, he'll try to attack and kill you. He can teleport, spawn mobs and is just generally a scary dude.