Blood Moon



A Blood Moon is a common, randomly occurring event that takes place over the course of an entire night. It causes several hazards for its duration: Enemy spawns increase, even near your Home and NPCs (where enemies do not normally spawn), Zombies become able to open Doors, and Bunnies, Penguins, and Goldfish transform into dangerous enemies, along with other effects (see below). Blood Moons are signaled by the message "The Blood Moon is rising..." in the lower left corner of the screen, and the moon, sky, water, and rain will appear red for their duration.

A Blood Moon will only occur if at least one player in the world has over 120 life, and only on nights when a moon is present (any night except a new moon). Given those criteria, a Blood Moon has a 1 in 9 chance (11.11%) of occurring. Without taking the current moon into consideration, there is an overall chance of approximately 1 in 10 (1/9 * 7/8 = 7/72, or 9.72%).

Enemies

 * The spawn rate of monsters on the surface increases, and The Groom has a chance to spawn. Enemies not only spawn faster, but more are spawned than can normally exist on-screen at once. This works no matter the environment, so Corruption enemies can also swarm even more than they normally would, for example.
 * Enemies can spawn even near NPCs and their houses, whereas those usually suppress enemy spawns.

Sold items

 * The Merchant sells Throwing Knives
 * The Arms Dealer sells Silver Bullets
 * The Clothier sells the Mime Mask. On the console version, he will sell George's Tuxedo for male players and Fabulous Outfit for female players
 * The Dryad stops selling Purification Powder, Sunflowers, and Grass Seeds, and starts selling Vile Powder, Corrupt Seeds and Crimson Seeds. If you have the console version, she will sell you Sparkly Wings
 * The Painter sells Evil Presence painting
 * The Steampunker sells Purple Solution (if the Corruption is present) or Red Solution (if the Crimson is present) instead of Green Solution
 * The Cyborg sells Rocket II ammunition.

Other effects

 * Deathweed blooms. Blood moons are the only time you can harvest Deathweed Seeds from Deathweed.
 * Most NPCs have their own unique lines commenting on the event. Female NPCs act annoyed or rude (except for the Party Girl).
 * All water will turn a blood red color in all biomes except for the Ocean. If it is raining, the rain drops will also appear red.

Tips

 * A Blood Moon only affects the surface. Players can avoid it entirely by staying underground.
 * During a blood moon, every enemy has a 0.1% chance of dropping the KO Cannon.

Trivia

 * One of the "Seven Signs of the Apocalypse" in the Bible states, "...on the 6th sign the moon will arise, showing the color of blood, bringing with it the demons that prowled the Earth, but were sealed away. Then they will feast on those who doubted...".
 * In real life, the Moon appears red during lunar eclipses, and is sometimes referred to as a "Blood Moon". As sunlight passes into the shadow through the atmosphere, the Moon is given a red/orange color due to the amount of air the light passes through. It is the same phenomenon that gives sunsets and sunrises such colors.
 * When a real Blood Moon occurred on 14 April 2014, a warning was jokingly announced on the official Terraria forums.

History
And its scary