Spawn describes the process of a mob or spawned object entering the game world. This can happen due to various causes — most mobs killed by players return after a certain time (this is called respawn), other mobs come into existence when their preconditions are met (e.g. certain attacking mobs on a patrol quest). Depleted Resource Nodes also respawn after some time.
When players first enter a new area, and some time ago other players killed many mobs (e.g. to fulfill a quest), the new arrivals may easily be surprised by respawns. This effect is alleviated by the fact that right after a respawn, mobs stand still and do not attack for about 5 seconds. This gives players enough time to move out of the aggro radius, if they react quickly.
Mob respawn time
Most normal mobs usually are on a 5 minute respawn timer. This may be different depending on the area and mob types aswell the population of players within the area. Additionally, since Wrath of the Lich King, if an area is heavily farmed and the mobs are killed very quickly right after they spawn, the game may switch to a fast respawn mode for that area (which means that mobs and resource nodes return much more quickly, usually within one minute). Looting or not looting creatures and npcs does not matter, it all depends on the different spawn timers.
The following is an overview of mob types and their usual respawn timers:
- 5 min
- Fast Respawn
- Usually 1 min
- Named mobs
- Normal named mobs may either be on the regular respawn timer, or they may be rare mobs, with timers of several hours or more (e.g. Broken Tooth). Generally, named mobs that are the object of quests will have a regular spawn timer while those that are guaranteed to drop quality loot will take longer.
- Instance trash mobs
- In instances, trash mobs usually are on a 2 hour respawn timer. There may be exceptions; instance designers sometimes use short respawn timers to create an extra challenge (e.g. Ancient Core Hounds). In raid instances, trash mobs are usually "bound" to a boss, and after that boss is killed, the trash will not spawn any longer.
- Instance bosses
- Instance bosses do not have a respawn timer at all. They only return on instance reset.
Note: While actions like skinning cause corpses to disappear, there is no evidence that this makes the mob respawn faster.