Mob AI

Each type of mob in minecraft has a certain AI (Artificial Intelligence) system with different behaviors and mechanics. Passive mobs will flee in random directions after being hurt, while hostile mobs will face and chase/attack the Player as soon as they come close. Neutral mobs will remain neutral until a player or mob attacks it, at which point the neutral mob will turn hostile toward and attack the entity/mob that hit it.

All mobs randomly walk around. When they come to a one block high wall, they jump. They avoid falling 4 or more blocks (falling 4 or more blocks means taking fall damage). All Mobs can float on Water.

Passive Mob AI
All passibe mobs can spawn in different kinds of biomes (except for Mooshrooms who only spawn in Mushroom biomes and Villagers who only spawn in Village structures). Every passive mob can spawn either as an adult or baby, except for villagers who always spawn as adults and cannot breed.

Mobs following player holding food will also pathfind.

Sheep
Sheep will walk around the world aimlessly. They will eat grass from grass blocks at times, (making the grass block a dirt block), resulting in their wool growing back if it was sheared. They can breed with Wheat.

They will also follow any player holding wheat.

They can spawn with different wool colours, and can be bred items like dyes to get different wool colours.

Cows
Cows will walk around the world. They can breed with wheat and will swim over deep water.

They will also follow any player holding wheat.

Pigs
Pigs will walk around aimlessly. They can breed with carrots, potatoes or beetroots.

They will also follow players holding carrots.

Mooshrooms
They only spawn in Mushroom biomes. They can breed with wheat, resulting in a mooshroom baby. They will sink in water, except for babies which will sink and drown. They can be sheared, resulting in a normal cow. Only adult mooshrooms can be sheared, because the young ones have grown mushrooms at their back..

Chickens
Chickens will walk around the world. They can be bred with wheat seeds, pumpkin seeds and melon seeds. They will follow players holding these seeds. They will swim in water. They are immune to fall damage.

Villagers
They will spawn in villages, and each profession (each profession will wear the respective robe/apron) in the corresponding house. They will randomly talk with teach other or the player by facing it and doing noises(grumps).

They run away from any monster mob (hostile mobs and all neutral mobs but wolves) at high speeds.

They can be breed by building a house, four walls and a door.

Ocelots
They naturally spawn on Jungles and nearby places. They run in response of the movement of the player. They can be tamed by feeding it a raw fish.

Wolves
Wolves can spawn in taiga or snowy spruce forests. Wolves may also spawn as babies. They will walk around the world, but if the player will attack one, the horde will go after the player and kill it (they will also change their eyes colour to a red). It can swim, except for baby wolves wich will sink and drown.

If tamed with bones, they will become a Tamed Wolves/Dogs (see Tamed Mobs Ai).

They won't breed, although they can be fed meat.

Endermen
Enderman will walk around the world, pick certain blocks like dirt or grass blocks and put them back in various places and teleport. If the player attacks them or looks at them (looking at them works only in Survival), they will start staring at the player, followed by them attacking him by teleporting, and homing in them from behind. They will also be hurt by water, and so they will teleport as soon they fall in it. However, unlike PC, Endermen will sometimes continuously walk into the water rather than stay away from it.

Zombie Pigmen
As of 0.12.0, Zombie Pigmen are changed to neutral. They ingnore the player it he/she enters its line of sight. But provoked, any loaded Zombie Pigman will attack the player in a given amount of time until they become passive again. They are immune to fire damage.

Before 0.9.0
Zombies spawn at night and attack the player as soon they see it. They will not pathfind, so they can be tricked in traps easily. They will start burning in daylight.

After 0.9.0
Zombies spawn at night or in Dark Places and will walk around. As soon as they see a player or a villager, they will attack it by homing and raising its hands. They will pathfind (avoid deep holes and lava). In daylight, they will start burning to death.

Skeletons
Skeletons will spawn at night or dark places and wander around the world. As soon as they see a player, they will circle to his left and shoot arrows. They burn during day.

As of 0.12.0, their AI us improved as they avoid direct sunlight to avoid burning themselves. They are usually found taking shelter from a tree of any place with a solid block above them. They also move to the closest water block to avoid getting burned.

Creepers
Creepers spawn at night or in dark places and wander around the world. They will follow the player, circle to its left and explode making a 'hissss' sound before exploding. They can forced to explode by using a Flint and Steel.

Silverfish
Silverfish will spawn in 'corrupted blocks' like stone blocks or bricks. These are called Monster eggs. They can also spawn because of the Stronghold's Mob Spawner. They will attack the player if spotted. If the player attacks back, all the hidden silverfish will destroy their block and go to the player. If left alone, they will tend to walk around, and corrupt other blocks.

Spiders
Spiders will spawn in dark areas or at night. They will follow the player and attack by jumping at him if spotted. They will pathfind and avoid traps, holes if possible. During they, they will become neutral, if the player didn't attack them.

Slimes
Slimes hope around the world. They can be in small, medium or big variant. When killed, smaller slimes will spawn.

Blazes
Blazes spawn in the Nether Fortress. They attack player with fireballs, burn the player for a while. The fireballs will set blocks on fire when contact. They can take damage by snowballs.

Ghasts
Ghasts spawn naturally in The Nether. They shoot big fireball to the player, cause a small explode and ignite blocks. The fireballs can deflect if player hits it or use projectiles.

Wither Skeletons
Wither Skeletons spawn naturally in the nether at nether fortresses. They walk slowly, but once they spot the player, they quickly run towards him/her to attack. They attack with their stone sword, which will effect the player with the Wither Status Effect. Wither Skeletons are 3 blocks tall and 1 block wide.

Tamed Wolves (Dogs)
These are obtained if a Wolf is tamed, making them get a red collar and friendlier eyes. They can be bred with meat, resulting in a baby tamed wolf/dog. If the dogs are low on health, they will keep the tail down. They wont be able to breed until they are healed by feeding them meat. If at full health, they will keep their tail up.

Wild baby wolves can also be tamed. They can swim (except for baby dogs which will sink) and will shake off the water after getting out of it.

They will follow its owner, obey if told to stand up/sit down and attack any mobs their owner is attacking/any mob that attacked its owner.

Ocelots (Cats)
When tamed, they follow the player, similar to a tamed wolf. Any creepers with a 15 block radius will avoid the tamed ocelot. They can be told to sit/stand on the command of the player