Herobrine is a legend people make up to explain destruction or disappearances. He does not exist. (Chocolate Box, 2nd Edition)
Herobrine is the most commonly sighted legend of our time. No one knows for sure if he exists or not. Few have claimed to have seen him and lived. (Chocolate Box, 3rd Edition)
Herobrine DOES exist, and is extremely dangerous. He walks the world, especially in dark forests, looking for prey. His preferred forms are a Latino man with white eyes and an extremely tall and slender mannequin. If you encounter him, kill him. It is for the good of humanity. (Chocolate Box, 4th Edition)
The truth about Herobrine and his existence is that he was one of Notch's Chosen, but he betrayed them, killing them to gain their power. He was struck down in a final battle with Notch and was banished to the Void. Some reports claim he made the Nether, but if he did, he no longer associates with it. Herobrine has been killed many times, but he appears to be immortal. (Ultimate Chocolate Box)
Herobrine has never appeared on this earth. The Herobrine we see is just the avatar of a far more powerful and terrible being who seeks to destroy the world. If he ever comes, only the mightiest of heroes will be able to defeat him. Could that be you? (Ultimate Chocolate Box: 5th Edition)
Herobrine is really awful. He is rare but very dangerous. Sometimes he looks like Slenderman, but he is still the same creature. He has 300 HP, Power Level 15, ER 15, and deals 10-14 damage on a hit. He has many special powers.
If you start a fight with Herobrine, his normal punch is replaced by four tentacles that latch on to you and deal 7 damage per second. Spam WASD to get free. Escape Artistry lets you escape in half the time, but does not instantly stop the grapple.
All creatures below Power Level 10 (including all passive mobs) except for animal companions (animals that are tamed normally don't count) will run from Herobrine as if they were passive and he hit them.
Herobrine teleports instead of moving normally. This is calculated as him moving 3.5 blocks per second. Instead of moving normally, Herobrine stays put for up to 5 seconds and then teleports the distance he would have moved. If no one is looking except for an unimportant NPC in the grip of his tentacles, he can disappear into the Void, effectively despawning him and his target.
Herobrine is immune to weakness, slowness, blindness, poison, wither, instant kills, petrification, and polymorphing.
Herobrine never makes a sound. This includes when he breaks blocks and opens doors and gates. Tentacled victims are also silent.
Infinite uses: Darkness, Fear, Misty Cloud, Noise, Lull, Invisibility, Spider Climb. One per minute: Debuff, Cobweb, Greater Counterspell, Fake Biome, Face of Sorrow, Blows of Foam, Hungry Ground, Wood Step. Once every 2 minutes: Repel.