Herobrine

Herobrine is a creature and one of the first enemies in Area 1.

Appearance
Herobrine looks like the minecraft default skin, Steve, but with white eyes. He carries a single diamond sword and wears textured-on clothes, and does not have any real animations.

Behavior
Herobrine will walk directly towards the nearest player to him in a large distance, ignoring walls or anything else in the way. This causes him to get stuck on many surfaces, doors, and such, partially due to his sword having collisions.

Once he reaches the player, they unceremoniously die on contact with herobrine, after which he immediately finds another target if applicable.

Appearances
He will appear in the most early parts of the game primarily, acting as a low-power threat in Area 51. Once the game begins 'kicking up', his appearances will be scarce if at all unless led on by a player.

Strategies
Herobrine is an extremely easy threat to avoid. As he follows the most basic AI Pattern in the game, turning corners quickly and locking doors behind you will almost completely negate him as a threat to the player.

Trivia

 * Herobrine's Sword has collisions, which makes him slightly more threatening as the sword does damage, but also less dangerous because it gets him stuck.
 * Herobrine was the first enemy added to the game.

Second Form
Herobrine has a second form rarely seen that is significantly more threatening.

Appearance
Herobrine looks almost identical to his first form, with the exception of much longer limbs. His head is also tilted down slightly, staring at whatever his target may be.

Behavior
Herobrine acts significantly different from his first form. He still moves toward the player (albeit at a slightly slower pace), and will not regard walls or doors in his way, though now has the ability to teleport at will. This makes him perhaps one of the most deadly enemies in the game if a player is not prepared for him, as he is capable of sudden jumps and instant kills.

His attack is also surprisingly long range, and he can grab and kill you from over 10 studs away.

Placing your mouse over him will cause him to stop moving entirely, until you move too far away or he teleports away.

Strategies
If you hear his notable glitch-like teleport sound, immediately scan the surrounding area and be ready to recoil at any door you open. He has a tendency to hide behind doors to ambush the player.

If you cannot hear his sound (as a player must already be extremely close to herobrine to hear it) then you should still be ready to check all doors and hallways you're near to prevent almost certain unexpected death by herobrine.

It is important to note that putting doors and walls between you and him does nothing, and will only deter him for a moment at most.