Herobrine should be a boss battle. When you make the summoner and drop a totem of undying on it, you will get teleported to a huge arena where herobrine will descend down on you. Then he will do loads of attacks. Lightning strikes, corruption shockwave, fireballs, summoning zombie-brines (herobrine zombies), splitting the ground open, and dashing at you with his diamond sword. He will have 1000 health and will be one of the hardest bosses in the game.