Mobs and drops | Citadel docs

local cow = world.spawn("cow", vec3(4.5, 65, 8.5))

nil where this game has no such kind

cow.id

entity id, what players.on_click reports in hit.entity_id

cow.name

"cow"

cow.at

vec3, live; nil once it is gone

cow.rotation, cow.hostile

cow.health, cow.max_health

its health now, and the most its kind gives it

cow.alive

is it still in the world

cow:destroy()

takes it out on the next tick

world.entities { mob = true }

every mob in this room, as handles

world.entities { mob = false }

every entity that is not a mob

world.items()

the stacks on the ground: { { id, item = "dirt", count = 3, at = vec3 }, ... }

A mob acts on its own on both kinds of server, lite included.
Each read gets the entity’s current state. Check alive.
A mob a pack spawns stays when the script reloads. An NPC does not.
tostring(cow) is entity(cow, 7): the kind’s name and the id.
A mob has the same handle as every entity the world moves: cow.velocity, cow:push(v) and cow:nearby(8) work too. See “Custom entities”.

a0.1.0 spawns nothing on its own. On an Alpha world every entity in world.entities { mob = true } comes from a dungeon spawner, /summon or this call.