Entity
Entities encompass all dynamic, moving objects throughout the Minecraft world.1
A mob is an AI-driven game entity resembling a living creature. The term "mob" is short for "mobile entity".1 All mobs can be attacked and hurt (from falling, attacked by a player or another mob, falling into the void, hit by an arrow, etc), and have some form of voluntary movement. Different types of mobs often have unique AI and loot.2
Spawning
Mobs spawn in various ways. Most mobs spawn naturally, depending on the light level, biome, and their surroundings. For example, most animals are found in bright areas on the surface, while hostile monsters are commonly found in the dark (whether it's a cave, dungeon, mansion, or at night). Animals usually spawn upon chunk generation, while hostile monsters spawn and despawn in certain radii around the player. Some mobs including passive and neutral animals have the ability to be bred by the player, creating offspring. Villagers also breed randomly depending on the time of day and the number of beds. Most mobs never spawn on transparent blocks, in water, in lava, on bedrock, or on blocks less than a full block tall. The exception is monster spawners, from which monsters can spawn naturally on any block including air.
Some mobs require that the player "construct" them before being able to spawn.2
Behavior
Mobs are affected by the environment in the same ways as the player; they are subject to physics, and they can be hurt by the same things that harm the player. When mobs are killed, they turn to dust and drop items that may be useful resources. Each type of mob in Minecraft has a certain AI (artificial intelligence) system with different behaviors and mechanics. Mobs ordinarily wander around at random if there is a player within 32 blocks and usually avoid walking off blocks high enough to cause falling damage. Many mobs have an advanced path-finding system that allows them to navigate through obstacles to get to a desired object or destination. Passive mobs flee in random directions after being hurt, while hostile mobs face and chase/attack the player as soon as the player comes close. Neutral mobs remain neutral until a player or mob provokes it (usually by attacking), at which point neutral mob becomes hostile toward and attacks the entity that hit it. Most mobs are aware of players within 16 blocks of them, but some can see farther.
Most mobs cannot see through most solid blocks, including semi-transparent blocks such as ice, glass, tall grass, or glass panes.2
List of entities
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Source: Minecraft Wiki. ↩↩
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Source: Minecraft Wiki. ↩↩↩