Spawn Rules

spawn_rules/*.yml spawn rules define under which conditions a custom mob appears. Spawn rule files live in plugins/EmakiMobs/spawn_rules/*.yml. Each file can contain multiple rules under a rules: list. A missing file, a missing rules key, or a rules value that is not a list produces no rules at all. The rules released on first start are spawn_rules/overworld_elites.yml (a single natural rule)

File structure

rules:
  - mob_id: <mob id>
    type: <spawn type>
    # type-specific fields...

Only two type values are accepted

The current loader recognises only type: natural and type: autonomous. Writing structure, biome, player_relative, day_interval, custom or anything else does not raise an error — it is logged as Unknown spawn type and the whole rule is skipped silently. A missing mob_id or type skips the rule with a WARN

Two rules in the bundled reference file spawn_rules/overworld.yml are never loaded

That file lives inside the plugin jar and is not released into plugins/EmakiMobs/spawn_rules/ (the first-start release is overworld_elites.yml). It holds three rules: the natural one (elite_zombie) works, while type: structure (bone_lord) and type: biome (jungle_stalker) hit the unknown-type branch above and are skipped silently. Rewrite those two using the natural / autonomous forms documented here if you copy the file

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natural — intercept vanilla spawn events

Replaces naturally spawning mobs with a custom mob by probability once the conditions hold. Natural spawns are intercepted at PreCreatureSpawnEvent (before the entity is created); other spawn reasons that are neither NATURAL nor SPAWNER are intercepted at CreatureSpawnEvent, which is cancelled

- mob_id: elite_zombie
  type: natural
  biomes: [plains, forest]   # optional biome restriction; empty means any
  y_range: [-64, 50]         # only replace within this Y range
  light_level_max: 7         # inclusive light level ceiling
  replacement_chance: 0.08   # replacement probability, 0.0–1.0
  max_nearby: 3              # max same-id mobs within 64 blocks; 0 = unlimited
  count:
    min: 1
    max: 1

Field	Type	Required	Default	Accepted values	Description
mob_id	string	Yes	none	a loaded mob definition id	The mob to spawn; a missing or non-string value skips the whole rule. An unregistered id spawns nothing
type	string	Yes	none	natural	Fixed value
worlds	string list	No	[] (any)	world names (World#getName)	Restrict to these worlds
biomes	string list	No	[] (any)	biome keys, optionally namespaced (the part after : is taken, lower-cased)	Restrict to these biomes; an unrecognised name logs a WARN and is dropped while the rest of the rule still applies
y_range	int list [min, max]	No	[-64, 320]	read positionally: item 1 is min, item 2 is max; missing items fall back to the default	Y range of the spawn position (inclusive)
light_level_max	int	No	15	0–15	The spawn position's combined light level must not exceed this; the default 15 means no restriction
replacement_chance	double	No	1.0	—	Replacement probability once conditions match: 0.0 never replaces, ≥ 1.0 always replaces (not clamped)
max_nearby	int	No	0	≥ 0; 0 = unlimited	Skip the trigger once this many same-id managed mobs exist within 64 blocks
count	{min, max}	No	{1, 1}	min ≤ max	Mobs spawned per trigger (random range, inclusive). min > max throws when the rule fires, so that replacement fails
condition	section	No	none	a CoreLib condition block	Extra conditions. There is no player context, so player placeholders cannot be used here (unlike autonomous)

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autonomous — self-scheduled spawning

Runs entirely outside vanilla spawn events, driven by its own scheduler. trigger selects the scheduling mode. Candidate positions are generated at a random angle at distance from the player, with up to 6 attempts, requiring a passable block above solid ground — so not every attempt produces a spawn

- mob_id: elite_zombie
  type: autonomous
  trigger: interval
  interval_ticks: 1200
  worlds:
    - world
  biomes:
    - plains
  distance:
    min: 16
    max: 64
  max_nearby: 4
  max_global: 10
  count:
    min: 1
    max: 2

The four triggers

trigger	Scheduling	Key fields
interval	Global fixed rate (first run 1 tick after start); each round scans every online player and attempts once per player	interval_ticks, worlds, max_global
player_follow	Global fixed rate; each round picks one random online player and attempts once	interval_ticks, worlds, max_global
day_interval	Checks each world's in-game day counter every 20 ticks (last trigger day stored per world) and attempts once for every player in that world when due	interval_days, on_day_start, worlds, max_global
cron	Fires on real system time via a Cron expression and attempts once per online player	cron, worlds, max_global

trigger values are case-insensitive. cron uses the 6-field Quartz format (second minute hour day-of-month month day-of-week), documented in CoreLib expressions - Cron; a blank or unparsable expression is logged as a warning and the rule never fires

autonomous fields

Field	Type	Required	Default	Accepted values	Description
mob_id	string	Yes	none	a loaded mob definition id	The mob to spawn; a missing or non-string value skips the whole rule
type	string	Yes	none	autonomous	Fixed value
trigger	string	Yes	none	interval / player_follow / day_interval / cron (case-insensitive)	Scheduling mode. Missing or unknown skips the whole rule with a WARN
interval_ticks	long	No	600	≥ 1 (ticks)	Scheduling period for interval / player_follow
interval_days	int	No	1	≥ 1 (in-game days)	Interval in in-game days for day_interval
on_day_start	boolean	No	false	true / false	When true, only fires while that world's time is < 1000 (just after sunrise); when false, it fires as soon as the counter is due
cron	string	No	""	a 6-field Quartz expression	Expression for trigger: cron; when blank a warning is logged and the rule never fires
worlds	string list	No	[] (any)	world names	Restrict to these worlds
biomes	string list	No	[] (any)	biome keys (same as natural)	Restrict the spawn position's biome
structures	string list	No	[] (any)	NamespacedKeys such as minecraft:stronghold	Restrict to positions inside that structure's bounding box in the chunk; an unknown structure logs a WARN and is dropped
y_range	int list [min, max]	No	[-64, 320]	same as natural	Y range of the spawn position (inclusive)
light_level_max	int	No	15	0–15	Combined light ceiling. Only checked when the value is below 15; the default 15 skips the light check entirely
time_of_day	string	No	any	any / day (1000–12999) / night (≥ 13000 or < 1000) (case-insensitive)	Restrict the time of day; an unknown value behaves like any
require_surface	boolean	No	false	true / false	When true, the spawn position must have sky light 15
distance	{min, max}	No	{16, 64}	≥ 0 (blocks)	Spawn distance from the player (inclusive); when min ≥ max the value is fixed to min
max_nearby	int	No	0	≥ 0; 0 = unlimited	Max same-id managed mobs within 64 blocks
max_global	int	No	0	≥ 0; 0 = unlimited	Global cap on same-id mobs across all worlds; when reached the whole round is skipped
count	{min, max}	No	{1, 1}	≥ 1	Mobs spawned per trigger (random range, inclusive); when min ≥ max the value is fixed to min
condition	section	No	none	a CoreLib condition block	Extra conditions; the player that triggered this attempt is the context, so PlaceholderAPI placeholders are rendered

How this differs from natural

A natural rule's condition has no player context, while an autonomous rule renders placeholders from the player being attempted. Both types collapse count and distance to a fixed value when min and max are equal