Pirate Invasion

The Pirate Invasion is a hardmode event where pirate themed enemies spawn and swarm the map's original spawn point. A Pirate Invasion can occur after certain conditions are met, or alternatively, when the player uses a Pirate Map which has a chance of dropping from enemies killed within an Ocean biome.

Criteria
The criteria for a random Pirate Invasion to occur is as follows:
 * No other events are currently in progress.
 * The Wall of Flesh must have been defeated.
 * At least one Demon Altar or Crimson Altar must be destroyed.

Chances

 * First, the Goblin Army event must fail to occur. (59/60 chance)
 * Then, there is a 1/30 chance that the Pirates will invade that day if they haven't invaded yet, otherwise the chance is 1/50
 * The final probability comes out as 3.27% each morning for the first invasion and 1.96% for subsequent ones.
 * You will get a random invasion about every 20 hours and 20 minutes of playing Terraria.
 * If, however, there is another invasion in progress, then there is no chance until the other invasion ends.

Initial Event
When a Pirate Invasion spawns or is summoned using a Pirate Map, a message will appear saying that "Pirates are approaching from the (East/West)!"

The message will repeat several times until the Pirates reach the initial spawn of the world or any area of the world above the surface which has a nearby NPC. When the Pirates' initial wave reaches the spawn, their arrival is announced with "The Pirates have arrived!" The music track "Golem" will then proceed to play as the players fight the pirates.

Pirates drop several kinds of loot; of particular note is the Cutlass, which has a high enough speed to outclass the Excalibur in DPS (damage per second). It is dropped by any pirate invasion creature but the parrot. Pirates also randomly drop Golden Tables, Golden Chairs and other golden pieces of furniture, as well as a pirate-themed vanity clothing set.

Completing the Event
Similar to a Goblin Invasion, you are required to defeat a large number of pirates in order to end the invasion. This may require the player(s) to kill many Pirate Captains. For a single-player invasion, the player is required to kill 120 Pirates before the event is completed, and this number increases with each additional player.

This is currently the Invasion rated for the highest-tier equipment in Terraria. Enemies have higher damage and defense than other invasions, but due to the limited AI, they might actually be easier than the goblin invasion for a weak but prepared player to overcome.

Defeating your first pirate invasion unlocks the Pirate NPC.

Trivia

 * The pirates are the only human enemies. (Besides the Nymph, which initially appears as the Lost Girl)

Tips

 * Pirates are essentially a harder version of the Goblin Army. Many of the same tactics and preparations will still prove effective.