Goblin Army

The Goblin Army, also known as the Goblin Invasion, is a random event within the game when goblins will attack a player. The Goblin Army will spawn at a 6.666% chance (approximately 1 in 15) at dawn if you meet the criteria stated below.

After multiple warning messages (tentatively spanning hours) 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. After 1.0.3, the new max of players is 255, meaning a max of 12,850 goblins.

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

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

Criteria
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 (NOT maximum).
 * You must have smashed at least one Shadow Orb.
 * You must not have had an invasion within 7 in-game days.

Video
A short demonstration of the Goblin Army.

Strategies
An open, flat space seems to work best for dealing with the Goblin Army, either on solid ground with no caverns or on an airborne platform. This allows you to easily deal with the fighters (they won't jump around and will be lined up for multiple hits) and help you get to the casters and dodge/destroy their missiles more easily. Also hit the projectiles with a sword and you may get a heart. Extremely shallow lava moats are also useful, as they will deal a fair amount of damage to enemies, but will not destroy item drops.