Blood Moon Horde

The Blood Moon Horde is a special Horde which only occurs during the Blood Moon, which on default settings occurs every 7 days (this is modifiable; see below). The name of the game is a reference to this every-seven-day attack.

The descriptions below are accurate as of Alpha 18.4 and except where noted assume default game settings and no installed mods.

General Concept
A Blood Moon Horde consists of an early-morning indicator, late-afternoon warnings, an initial attack followed by subsequent waves of attack, and the conclusion at 4AM. The zombies spawned during a Blood Moon Horde know exactly where you are regardless of quiet, lack of heat, sneaking, or defenses. They will climb or dig as they are able in order to reach you. See below for general strategies to fight (or not) the flood of attackers.

Indicator and Warnings
At 0800 on Blood Moon day (this can be customized), the day number in the HUD will turn red. This is your first indication that the horde will be coming that night. At 1800 you will hear a crack of thunder and the sky will slowly start to turn red. By 2100 the sky will be very red and the storm will be in full swing. You are definitely running out of time!

Initial Attack at 22:00
At 22:00 there will be a directionless scream announcing the beginning of the horde. Shortly thereafter a number of zombies will spawn some distance away from you and run towards you. The exact number of zombies depends on several factors including your Gamestage, the number of players if multiplayer, and performance settings. See below for details.

Subsequent Waves
As you kill zombies, more will spawn to take their place. Eventually you may kill an entire wave in which case after a short delay a new wave will begin to arrive. Each wave also has its own timer such that if you can't kill the entire wave in time it will stop spawning and the next wave will begin. This is generally invisible to the player, but see below for details.

Conclusion at 0400
At 0400 the Blood Moon Horde will end. The sky will turn from red to clear and horde-spawned zombies will return to normal behavior (slower movement, no GPS to you).

Blood Moon Frequency
On default settings, the Blood Moon will occur every 7 days. Both single-player and dedicated server games can modify this (or disable it entirely). The two related settings are:

Note that each Blood Moon Frequency setting is relative to the previous Blood Moon. The next blood moon occurs on frequency +/- the range.

Example 1: Setting frequency to 7 and range to 1 means that the first Blood Moon might occur on day 6, 7, or 8. If the Blood Moon is on Day 6, then the next Blood Moon might occur on (6 + 7 +/- up to 1 day), meaning days 12, 13, or 14. Example 2: Setting Frequency to 10 and range to 3 means that the first Blood Moon could be on days 7-13. If the 1st occurs on day 8, then the 2nd will occur on (8 + 10 +/- up to 3 days), meaning days 15-21. Example 3: Setting Frequency to 1 will cause a Blood Moon every night, if you're into that sort of thing.

Simplified
The simplified version of the mechanics are this:
 * 1) Number and strength of waves is determined by your gamestage
 * 2) The number of actual zombies you will fight at any one time is determined by gamestage, number of players, and game settings
 * 3) Each wave has a total number of zombies and a timer - either killing an entire wave or running out of time will start the next wave (any remaining unspawned zombies in the current wave will not spawn)
 * 4) As of Alpha 18.4, the waves are finite; if you can kill all of the zombies in the final wave there will be no 'trickle' of zombies the remainder of the night (it can be added back in through a modlet, however)
 * 5) At 0400 all remaining Blood Moon-spawned zombies will revert to normal behavior

The File Where it Happens: Gamestages.xml
The configuration file which controls Blood Moon Horde spawning is gamestages.xml. Here is an example for gamestage 59 which we will walk through. Each  line identifies a single wave of the overall horde.    Here is how to interpret the parameters in that block.

How Many Zombies Could There Be?
The total possible number of zombies which can spawn during a Blood Moon Horde can be found by adding up the 'num' parameter for all waves in the appropriate entry in gamestages.xml. In the example shown above, the total number of possible zombies is 84 + 84 + 84 = 252. The actual number of zombies spawned at the same time will likely be different and the total number of zombies actually fought might be different depending on how efficient you are at killing them.

How Many Zombies Will Spawn At Once?
The total number of zombies which will spawn at once - say, in the initial attack on your base - is the lesser of the following three values.

Example 1: In this example, the limiting factor is Blood Moon Enemy Count, so only 8 zombies will spawn from the horde at once. As they are killed, new horde zombies will spawn to keep the total at 8.
 * Single-player game
 * Max Spawned Zombies = 64 (default)
 * Blood Moon Enemy Count = 8 (default)
 * Parameter 'maxAlive' for the horde wave = 22
 * Parameter 'num' for the horde wave = 100

Example 2: In this example, now the limiting factor is the 'maxAlive' parameter for the horde wave, which is 22. As gamestage increases, eventually maxAlive will grow to be greater than the Blood Moon Enemy Count setting (32) and then the limit would be 32 at once.
 * Single-player game
 * Max Spawned Zombies = 64 (default)
 * Blood Moon Enemy Count = 32
 * Parameter 'maxAlive' for the horde wave = 22
 * Parameter 'num' for the horde wave = 100

Example 3: In this example, the limiting factor is Max Spawned Zombies. This is because 'maxAlive' (22) times the number of players (3) equals 66 total spawns. However the Max Spawned Zombies setting is 64, so only 64 spawns would happen at once.
 * Multiplayer dedicated server game with 3 players
 * Max Spawned Zombies = 64 (default)
 * Blood Moon Enemy Count = 32
 * Parameter 'maxAlive' for the horde wave = 22
 * Parameter 'num' for the horde wave = 100

Max Spawned Zombies Setting and Natural Spawns
At the beginning of a Blood Moon Horde there may be some natural spawns in the area. These spawns do count against the Max Spawned Zombies limit, and the Blood Moon horde will only spawn zombies until the max is hit, even if this is less than would otherwise be allowed. So in Example 3 above, if there were 10 naturally-spawned zombies milling around when the horde started, the horde would only be able to spawn in 54 zombies (64 max minus the 10 already in the world) to start with. Eventually the natural spawns will time out (or be killed) and pretty much all living zombies will be from the horde spawner.

Kill 'Em All vs Horde Wave Duration
Each horde wave has a duration expressed in in-game hours. In the example above the first two waves have a duration of 2 hours and the last has a duration of 7 hours. Note that the entire Blood Moon lasts for 6 hours, so a duration of 7 essentially means 'for all the time remaining until 0400'.

When fighting or evading the horde, there are three possible results for each wave:
 * 1) You kill all of the zombies in the wave (the 'num' parameter) - in this case the next wave will start immediately after the 'interval' parameter of the wave you killed
 * 2) You fight/evade the wave until its duration expires - in this case the next wave will start after 'interval'; any remaining zombies still must be killed or evaded
 * 3) You fight/evade the wave until 0400 - in this case all remaining zombies will switch to normal behavior and you can clean them up or evade them like any other zombie

If you repeatedly achieve result #1, it is quite possible to 'beat' the Blood Moon well before 0400. After that there will be no more spawns (see below). If you at least achieve result #1 on the final wave, you will 'beat' Blood Moon and spawns will cease. At higher gamestages this is increasingly difficult as the waves are more numerous and have a larger total spawn amount.

Multiplayer and Performance Considerations
The primary differences between single-player and multiplayer hordes are the per-player horde spawn limits. These are 'Blood Moon Enemy Count' and 'maxAlive' described above. Generally you will not want to mess with maxAlive unless you are building a mod, so to adjust the multiplayer experience you will want to adjust Blood Moon Enemy Count. Increasing the value will - especially as your gamestage passes about 50 or so - make the 'horde fight' bigger in a very direct way. Double the value and you will see double the zombies attacking your base at the same time. This has significant performance impacts for both the server and the clients.

The global setting affecting single-player, multiplayer, and performance is Max Spawned Zombies. Increasing this value will allow more zombies in your world at all times as well as lifting the ultimate cap for Blood Moon hordes. This is a hard limit for the entire game so, for example, in a 4-player game setting Max Spawned Zombies to 100 while having Blood Moon Enemy Count at 30 will not make a lot of sense, since the 4 x 30 = 120 desired max for Blood Moon will be capped by the game-wide Max Spawned Zombies setting of 100.

Customizations
The following customizations are just a sample of changes you can make to adjust the Blood Moon Horde to your liking.