Reactive World

About

Reactive World makes the Overworld react to player activity. When you hunt animals, the world remembers. When you over-farm your land, the soil wears out.
The more you exploit a species or a plot of land, the harder it becomes to sustain. Leave nature alone long enough, and it gradually recovers.

More features will be added over time…

Installation

• ⏩ Requires NeoForge to be installed: https://neoforged.net/.
• ⏩ Copy the jar file of the mod in the "Mods" folder.
• ⏩ For each version, check in the changelog the supported/tested versions of Minecraft and Neoforge.

Fauna Dynamics

Overview

The world's wildlife responds to how aggressively you hunt. Every kill is tracked per species, and natural spawn rates are suppressed the more you hunt. Stop hunting long enough, and the population slowly recovers on its own.

Affected Mobs

The mod tracks kills and affects natural spawns for the following creatures:

Bee, Axolotl, Cat, Horse, Goat, Pig, Dolphin, Camel, Frog, Llama, Rabbit, Wolf, Sheep, Mule, Ocelot, Polar Bear, Panda, Parrot, Chicken, Squid, Glow Squid, Fox, Armadillo, Tadpole, Cow, Donkey, Cod, Salmon, Tropical Fish, Pufferfish

Only kills made by players in the Overworld are counted.

How It Works

1. Kill Tracking

Every time a player kills one of the tracked mobs, the kill count for that species increases by 1. The game also records when the last kill happened.

2. Spawn Suppression

When a tracked mob tries to naturally spawn, the mod calculates the probability that the spawn is cancelled, using a sigmoid (S-curve) function:

Variable	Meaning	Default
K	Current kill count for that species	N/A
k₀	Kill count at which there is a 50% chance a spawn is cancelled	13
a	Steepness of the curve (how fast the penalty ramps up)	0.4

• At low kill counts (well below k₀), spawns are almost unaffected.
• At exactly K = k₀, 50% of natural spawns are cancelled.
• At high kill counts (well above k₀), spawns are almost completely suppressed.

3. Fauna Regeneration

The kill count for each species slowly decreases over time, representing the population recovering. This happens on a periodic timer, but only if you haven't killed any more of that species recently.

The regeneration formula applied each interval is:

Variable	Meaning	Default
r	Regeneration rate / fraction reduced per interval	0.02 (−2%)
Regen interval	How often regeneration is applied	72000 ticks (3 MC days)
Idle threshold	Minimum time since last kill before regen triggers = interval × multiplier	1.5× → 4.5 MC days

So if you stop killing Sheep, after 4.5 in-game days the kill counter starts dropping by 2% every 3 days, gradually restoring natural spawn rates. Once the kill count drops below 1, it is fully reset to zero.

Configuration

You can adjust these settings in the mod configuration screen from the Minecraft interface:

Key	Description	Default
sigmoid_k0	Kill threshold for 50% spawn suppression	13
sigmoid_a	Sigmoid steepness	0.4
regen_interval_ticks	Ticks between each regen step	72000
regen_interval_multiplier	Idle time multiplier before regen starts	1.5
regen_rate	% of kill count removed each regen step	0.02

Farmland

Overview

Farmland has a finite capacity to produce. Harvesting crops repeatedly without letting the soil rest will progressively exhaust the land. Over-farmed soil slows crop growth, and if pushed too far, dies entirely; turning back to dirt and refusing to grow anything until it has had enough time to recover.

How It Works

1. Exhaustion

Each time a crop is harvested on a piece of farmland, its exhaustion level increases by 1. By default, only fully mature crops trigger exhaustion (exhaust_only_on_mature_crop). Automatic harvests (pistons, water flows, etc.) can also be tracked if enabled.

• When a player harvests a crop, the farmland immediately converts to dirt, forcing re-tilling.
• When an automatic system harvests, the farmland only converts to dirt once the exhaustion reaches the maximum level.

2. Growth Penalty

Even before the land is dead, exhausted farmland slows crop growth. Each potential growth tick has a cancel chance determined by a configurable curve, based on the ratio exhaustion / max_exhaustion:

Curve	Formula	Cancel Chance Behaviour
SOFT	√(ratio)	High cancel chance from the first harvest, softens at high exhaustion
LINEAR	ratio	Steady, predictable cancel chance (default)
STEEP	ratio²	Low cancel chance at low exhaustion, punishing near max

3. Fallow & Tilling

When you try to till exhausted land, the mod checks whether a sufficient fallow period has passed since the last harvest:

• Fallow respected (enough time has passed): exhaustion decreases by 1. A green particle effect confirms the land is recovering.
• Fallow not respected (too soon): tilling succeeds but a warning message is shown with orange particles. The exhaustion level is not reduced.
• Dead land (exhaustion ≥ max, and dead recovery not yet elapsed): tilling is blocked. A smoke particle and an error message indicate the land needs more rest.
• Dead land recovered (enough time has passed since death): the exhaustion data is cleared and the land can be tilled normally again.

4. Dead Land Recovery

Once land has been pushed to its maximum exhaustion, it needs a long rest (dead_recovery_ticks) before it can be farmed again. During this period:

• Tilling is blocked.
• Crops cannot grow on this soil (even if somehow planted).
• Smoke particles indicate the blocked state.

After the recovery period, the next tilling attempt fully resets the exhaustion and restores the land.

Configuration

Key	Description	Default
fallow_ticks_required	Minimum ticks of rest between harvests before exhaustion stops increasing	48000 (2 MC days)
max_exhaustion_level	Number of harvests without sufficient fallow before land dies	5
dead_recovery_ticks	Ticks for dead land to fully recover	144000 (6 MC days)
exhaust_only_on_mature_crop	Only count exhaustion when harvesting a fully grown crop	true
track_automatic_harvests	Also track exhaustion from automatic harvests (pistons, water, villagers, etc.)	true
growth_penalty_curve	Shape of the growth cancel-chance curve (SOFT, LINEAR, STEEP)	LINEAR