The Goblin Army (also known as the Goblin Invasion and the Goblin Siege) is an Event when unique Goblin enemies spawn and swarm the map's original spawn point (not the spawn set by the Bed). A Goblin invasion has a random chance of occurring at any particular dawn, if the criteria stated below are met. It can also be triggered manually using a Goblin Battle Standard.
The criteria for a Goblin Invasion to occur at all is as follows: 
- You must have at least one person in the game with at least 200 current life.
- You must have smashed at least one Shadow Orb or Crimson Heart.
- After the spawn criteria have been met, there will be a 1/3 chance every day for the army to first invade.
- Further invasions (after the first has been defeated) have a 1/30 chance of occurring each day in normal mode and 1/60 chance in hardmode.
- You will see a random invasion about every 12 hours of playing in normal mode and every 24 hours of playing in hardmode.
- The Goblin invasion takes a higher priority than the Pirate Invasion, which can only occur when the Goblin invasion fails to do so.
When a Goblin invasion is coming, a message will appear reading: "A Goblin Army is approaching from the [east/west]!"
This message repeats a few times (Four times on a small-sized world, five times on a medium-sized world and six on a large-sized world). The direction specified in this message only pertains to the initial wave of Goblins, which spawns at the World's edge and travels to the player's original spawn point. Additional waves spawn immediately within the player's original spawn area when the player is in that area.
If the message says "West", the initial Goblins will come from the left. If the message says "East", they'll arrive from the right. Note that these directions are not related to the apparent motion of the Sun and the Moon, which, in Terraria, appear to move from left ("west") to right ("east").
When the Goblin Army is about to begin spawning around the player's spawn point, the following message appears: A Goblin Army has arrived! and the theme music will switch to the soundtrack "Boss 1."
Completing the event
The event is completed when the player(s) defeat all goblins in the army.
The size of the army is based on the count and health of the players currently in the world. There will be 80 base Goblins, plus an additional 40 for each player that has a maximum health of 200 or more. In single player, the army will consist of 120 goblins, while in an 8-player game, with each player having 200 HP or more, it will spawn 400 Goblins. With the maximum of 255 players above 200 health, the maximum number of goblins in an invasion is 10,280.
When the final wave of Goblins is on the screen, a message will appear saying A Goblin Army has been defeated!, and the theme music will return to normal after the last goblin is killed.
- Goblin Scout: An enemy Goblin that drops Tattered Cloth and spawns near the edges of the world. Tattered cloth can be collected and used to craft a Goblin Battle Standard, which is used to cause the invasion manually.
- Goblin Tinkerer: A Town NPC. Appears bound underground randomly after one goblin invasion has been defeated.
- Completing this event at least once can be essential to game advancement, as it makes the Goblin Tinkerer available.
- Dying will not end the invasion or cause any goblins to despawn.
- There must be no enemies on screen for the goblins to begin their attack.
- Goblins override the current biome's enemies in the same way as Meteor Heads.
- The invasion will not prevent most other events, so you may end up fighting the Goblin Army and a Boss at the same time. A Blood Moon or a Solar Eclipse may occur during a Goblin invasion, but their related mobs only spawn after the Goblin Army has been defeated.
- Goblin Peons will break doors instead of opening them. If the door belonged to a House containing your Bed or an NPC, this will cause your spawn point to reset or the NPC to move out.
- While the invasion event is active The Guide (and other NPCs) will not respawn. The goblins must be defeated and all other conditions must be right for normal respawns to occur (see NPC).
- Using the Goblin Battle Standard when a Goblin Army is already approaching will have no effect.
- Rarely (may be a glitch), a Goblin Army will approach without destroying a Crimson Heart/Shadow Orb.
- Because the goblins will only continue to spawn at the map's original spawn point, building your home elsewhere allows a player to avoid fighting the army.
- Piercing items like Spears and Flails can take out many goblins at once.
- 1.0.6: Can now be initiated with a Goblin Battle Standard.
- Pre-Release: Introduced.
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