Blood Moon



The Blood Moon is an event that has a 1 out of 9 chance (11.1%) of happening any night other than a new moon. That means that, if you don't know if it will be a new moon next night, there will be a 1/9 * 7/8 chance, or 7/72 chance (9.72%). It will only occur if at least one player in the world has over 120 life. It is heralded by the message "The Blood Moon is rising..." on the lower left side of the screen.



Blood Moon effects
Additionally, in hardmode:
 * The store Inventory of most NPCs change. The Merchant will sell Throwing Knives, the Arms Dealer sells Silver Bullets, the Clothier sells the Mime Mask, and the Dryad stops selling Purification Powder, Sunflowers, and Grass Seeds, and starts selling Vile Powder and Corrupt Seeds.
 * The spawn rate of monsters on the surface increases, and The Groom has a chance to spawn. The increase in the spawn rate includes not just the rate at which enemies spawn, but also multiplies the maximum number of enemies that can be on the screen at any given time (leading to sometimes impressive swarms). This works even when the player is not in standard environments, so Corruption enemies can swarm even more than they normally would as well.
 * Zombies become able to open a door after hitting it ten times. This can put the player's home and NPCs in peril if they are not guarded appropriately.
 * Enemies can spawn even when the player is near NPCs and his/her Home(s). NPCs usually have a cumulative effect of suppressing enemy spawn rates, and tightly clustered NPCs can usually prevent the spawning of any enemies at all within the radius of a few screens. During the blood moon this effect ceases in addition to the increased spawn rate, causing what appears to be an even more dramatic upswing in the spawn rate.
 * All Bunnies and Goldfish will become Corrupt Bunnies and Corrupt Goldfish.
 * Deathweed will bloom. Blood moons are the only time you can harvest Deathweed Seeds from Deathweed.
 * Female NPCs become unusually annoyed (the Nurse and the Mechanic especially). This is probably a crude joke based on "blood" and "that time of the month."
 * Possessed Armor can open doors, similarly to zombies.
 * Clowns have a chance to spawn.

Tips

 * The Blood Moon can benefit players by providing quick money and items.
 * Newer players may want to barricade themselves indoors during the event. Doors can be barricaded easily by placing blocks of any type directly next to them. Other placeable items like the Table or a Torch will prevent doors from swinging inwards, which is the only way Zombies and Possessed Armor may enter. Placing all doors at least two tiles above ground, or with a 2x2 trench in front of them, will also prevent intruders. The player can also place two doors next to each other to prevent the intruders from entering.
 * Newer players who want to pick a fight may do well to fight from within their own homes. Small caves also make decent areas to make a stand. Fighting from inside of one's house or any other enclosed space prevents zombies from spawning on both sides of the player (if fighting on open terrain), or dropping down from above (if backed up to a cliff), reducing combat to the mere slog of swinging one's weapon of choice continuously until dawn breaks.
 * More advanced players may want to go beyond merely putting their doors out of zombie reach and build lava "moats" to let zombies walk into. While unnecessary, and not even particularly profitable at the stage of the game where lava becomes available, many players find an endless stream of zombies walking into a lava pit and exploding quite amusing.
 * It is possible to place any block in front of or behind a door, open the door (or let it be opened/broken), and then wisely kill all of the zombies that attempt to get in.
 * Using Wire, one can easily set up a full base auto-lock-down system by placing Active Stone Blocks in front, or behind the doors, or as doors.
 * If a player has access to the Fish Statue, they can make a fish tank of some sorts, connect a 1 Second Timer and watch the corrupt goldfish spawn. This has two advantages: first and foremost, the massive amount of (corrupted) goldfish spawning will stop other mobs from spawning, and second, the player is able to make staggering amounts of money by killing all the corrupt goldfish. A Bunny Statue will also work, and will provide Bunny Hoods, which sell for 40 silver, in addition to the money dropped.
 * Using a Bunny Statue or a Fish Statue during a blood moon while in the underground hallow or corruption is a great way to quickly gather large amounts of souls of night and light.