Goblin Army

The Goblin Army is a random event within the game when goblins will attack a player. The Goblin Army will spawn at a 6.666% (approximately 1 in 15) chance at Dawn if you meet the criteria stated below. After multiple warning messages (occurring every half hour beginning at 6:00 am) the army will appear. The size of the army is based upon the count and health of the players within the game, according to the formula of 100+50x, with x being the number of players with a current of 200 HP or more. So, in single player, the army will consist of 150 goblins, while in a full 8-player game, with each player having 200 HP or more, it will spawn 500.

All Goblins in the invasion will together drop a total of about 8-10 gold

The army will be made up of the following goblins
 * Goblin Peon
 * Goblin Sorcerer
 * Goblin Thief
 * Goblin Warrior

The criteria for a goblin invasion to occur is as follows:
 * You must have at least one person in the game with 200+ current life.
 * You must not have had an invasion within 7 in-game days.
 * You must have at least one Shadow Orb smashed in your current map. It is reported that Shadow Orbs could be smashed automatically when the world was initially generated. So it is possible for the invasion to happen even if none of the players has smashed any Shadow Orb.

Interesting notes about goblin invasions
 * There must be no other spawned enemies on screen for the goblins to begin their attack, this was discovered after a long period of leaving the game open with a large pit for zombies. Upon coming back to the game, there were a number of zombies in the pit, and as soon as they were slain a goblin army began assaulting without warning (it is assumed the goblin warnings occurred earlier while away from the keyboard.
 * Goblins spawn in waves of 5, there will never be more than 5 on screen at once. This means if you trap 5 goblins in a hole, it is safe to move around or even go away from the keyboard, as long as the 5 goblins remain on screen at all times.
 * In some terrains, aforementioned waves fail to spawn at all. Example of such a terrain is a huge hill (higher than screen height) on the opposite side of the invasion, with player's character being directly under the hill. In such cases, no more waves will be spawned until player moves so that both sides of the screen are not fully covered with solid blocks.