You can tell a Blood Moon is out when the sky turns red. There is something about it that causes monsters to swarm.
"The Blood Moon is rising..."
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 the player's 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 the duration of the event. A reddish-pink filter will also be present in all above-ground areas.
A Blood Moon will only occur if at least one player in the world has more than 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 (11.11%) chance of occurring.
- The spawn rate of enemies on the surface increases. Dripplers , Blood Zombies , The Groom, The Bride , and the Clown (if in Hardmode) have 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 and Crimson enemies can also swarm even more than they normally would, for example.
- Enemies can even spawn near NPCs and their houses, whereas those usually suppress enemy spawns. Player-placed walls are not necessarily safe during this event.
- Zombies and their counterparts can open Doors.
- Goldfish become Corrupt Goldfish/Crimtane Goldfish , Bunnies become Corrupt Bunnies/Crimtane Bunnies , and Penguins become Corrupt Penguins/Vicious Penguins . Those spawned from Statues are Corrupt/Crimtane or Vicious , and they do not revert to regular Goldfish or Bunnies after the Blood Moon is over. If it is raining during the event, transformed Goldfish will flop around on the ground, rather than walk.
- The Merchant sells Throwing Knives.
- The Arms Dealer sells Silver Bullets (Pre-Hardmode. In Hardmode, the Arms Dealer will always sell Silver Bullets).
- The Clothier sells the Mime Mask, Fallen Tuxedo Shirt and Fallen Tuxedo Pants .
- The Dryad stops selling Purification Powder, Sunflowers, and Grass Seeds.
- The Painter sells the 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.
- The Skeleton Merchant sells the Slap Hand during Hardmode.
- Deathweed blooms. Blood moons (and Full Moons on Desktop, Console, and Mobile) are the only times you can harvest Deathweed Seeds from Deathweed (with the exception of harvesting with a Staff of Regrowth).
- Most NPCs have their own unique lines commenting on the event. All female NPCs except for the Party Girl act annoyed or rude.
- As said before, water will turn red, including Rain. A red filter will be applied to the screen as well, shifting the colors of all entities and light towards red and purple shades. This will also affect the projectile colors of many weapons.
- The Blood Moon's effects on enemy spawn rates stack with that of the Water Candle and Battle Potion.
- A Blood Moon only affects spawn rates above the surface. Spawn rates below the surface remain the same.
- Whether or not a Blood Moon will occur is determined at dusk each night.
- Every nightfall has an equal chance of being a Blood Moon and does not change if the previous night was a Blood Moon. It is possible to have four or more Blood Moons in a row and, conversely, a Blood Moon will not necessarily occur even over the course of many in-game weeks.
- In a multiplayer game, using the time adjustment server commands (dawn, noon, dusk, midnight) will not trigger the Blood Moon check, and so using "dusk" repeatedly does not force a Blood Moon to occur.
- Water in an Ocean biome will not turn red even though all other water in biomes will. However, the blue water is still affected by the red shader, giving it a purple color.
- If a player chooses to, they can cancel a Blood Moon by summoning the Pumpkin Moon or Frost Moon.
- A Blood Moon can happen in the middle of a Pirate Invasion. The invasion will still go on until it ends, then the Blood Moon starts. A Blood Moon can also occur during Slime Rain.
- Blood Moons occur more often than Solar Eclipses, as Solar Eclipses have a 5% (1/20) chance to happen each day (when the criteria are met).
- A different music track, Eerie, plays while a Blood Moon is active, as opposed to the usual Night theme. The theme serves to add a horror element to the event.
- If a Blood Moon and Full Moon coincide, Werewolves will spawn with increased frequency, rather than Zombies, but the special Zombies will still spawn.
- During a Blood Moon in Hardmode, every enemy and NPC has a 1 in 1000 (0.1%) chance of dropping the KO Cannon. This means that even though it is rare, like with the Blessed Apple, the large number of drop chances makes this easier to farm, and the KO Cannon is likely to aid a player in early Hardmode.
- Simply placing a block in front of a door will prevent Zombies from being able to open the door.
- If you see the notification that a Blood Moon is rising and you are under equipped to defeat it, get underground as quickly as possible. Going indoors will not save you. Neither will standing around outside. The Blood Moon gives enemies dangerous abilities, such as the ability to open doors or the ability to spawn within player-placed walls.
- Although the Blood Moon is typically treated as a deadly event, it is possible to enjoy the event. Once you've got max health and good weapons and armor, the new enemies are not a serious threat, especially if you've prepared your base. As the Tavernkeep says, "You know, where I'm from, a Blood Moon is actually just an excuse to get some fresh air."
- 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. This is the same phenomenon that gives sunsets and sunrises such colors.
- When a real Blood Moon occurred on April 14, 2014, a warning was jokingly announced on the official Terraria forums.
- During a Blood Moon, most female NPCs use more irritable or aggressive dialogue than normal. This is a reference to the fact that some women in real life become irritable or aggressive due to premenstrual syndrome, as both the menstrual cycle and the real-world Moon cycle occur approximately every 28 days.
- Information taken from the Desktop 18.104.22.168 source code, function
- www.terrariaonline.com → Forums → News → Dev Blog → thread: The Blood Moon is Rising...
- Desktop 22.214.171.124:
- The Bride, Blood Zombie and Drippler introduced, including their drops and banners.
- Improved atmosphere.
- The Skeleton Merchant was introduced, and sells the Slap Hand during the night of a Blood Moon.
- The Clothier sells the Fallen Tuxedo Shirt and Fallen Tuxedo Pants during the night of a Blood Moon.
- Desktop 1.2:
- Desktop 1.1: The chance of a Blood Moon was decreased to 1/9 from its previous chance of 1/7.
- Desktop-Release: Introduced.
- Console-Release: Introduced.
- Switch 1.0.711.6: Introduced.
- Mobile-Release: Introduced.
- 3DS-Release: Introduced.