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 Reach the original spawn. 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 HP of 200 or more. So, in single player, the army will consist of 150 goblins, while in an 8-player game, with each player having 200 HP or more, it will spawn 500. With the maximum of 255 players above 200 health, the maximum number of goblins in an invasion is 12,850.

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

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.

Another good strategy is to dig a pit deep enough so the Goblin Army cannot jump out, and buy about 80 grenades. Toss the grenades into the pit, and use a Minishark or other ranged weapon to take out the Goblin Sorcerers. This gives you an easy and humorous way to deal with the army.

A third possible strategy requires several buckets of lava and a long, flat, open space. Choose a point roughly in the middle of this space; this is where you will stand during the invasion. On either side of this space, dig a trench one block deep and ten or twelve blocks wide. Use your lava buckets to fill these trenches; three buckets for a twelve block trench is usually sufficient. After filling the trenches, test the lava depth by throwing a single copper coin into the lava. If your coin disappears, lengthen your trench by one block. Repeat the coin test until it no longer disintegrates in the lava. Now you need to check to make sure you have enough lava to cause damage; you can test this either with yourself (make sure you have at minimum 101 health) or by luring a monster in. Once your trenches are sufficiently filled, place two wooden platforms in the air several blocks above the trenches; make sure you can see the entire platform from your center space! If your setup is correct, the goblin army will spawn offscreen and die harmlessly in your trenches, the Goblin Sorcerers will spawn on the wooden platforms, wide open for a ranged assault, and the entirety of the loot will be waiting for you to pick it up from the traps.