🧬 Mutagen

Become the mob. Pay what it costs.

⚠️ EARLY ACCESS

This is 0.1 «First Dose», the first public release. The core loop is complete and playable, strains live in datapacks, the lab needs research, and from stage III the creature grows on your body.

• Loaders: Fabric & NeoForge
• Minecraft: 1.21.1
• Java: 21
• Strains in this build: zombie, skeleton, creeper

Required

• Architectury API
• Fabric API (Fabric only)

Recommended

• Pehkui — with it the body changes size through Pehkui: hitbox, eyes, reach and inertia. Without it the mod does the same with vanilla scaling.

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📖 About

Mutagen is not a morph mod. There is no key that turns you into a wolf.

To become something, you hunt it, take a tissue sample with a syringe, purify it in a centrifuge, synthesize a serum — and then keep dosing yourself for in-game days while your body slowly rearranges itself. A dose does not raise your progress. It fills an absorption reserve, and the body works through that reserve at 1% every 30 seconds. Stop dosing and the transformation falls back on its own: human nature takes its own back. The one exception is the full form — once the body has turned completely, there is no humanity left to pull it back, and only a reversal serum will.

By the end of that path you are no longer rendered as a player at all. You are also on fire in daylight, panicking near cats, or unable to keep armour on. Every ability in this mod ships with the price it costs, in the same version.

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🔬 The loop

hunt the mob  →  syringe  →  sequencer (read the species)
                          →  centrifuge  →  synthesizer  →  inject  →  live with it

1. Syringe — right-click a mob. It takes damage, it turns on you, and it will not give a second sample for ten minutes. A weakened, restrained or adult target gives better material; a mob from a spawner gives poor material. Golden and netherite syringes last and take cleaner samples. Quality carries all the way through to how strong your dose is.
2. Sequencer — spends samples and redstone to read the species' genome. You cannot synthesize what you have not read: 25% research allows a weak serum capped at 40%, 50% a full serum capped at 70%, 75% a serum that goes all the way. At 100% the strain holds without a stabilizer.
3. Centrifuge — burns ordinary fuel, turns a raw sample into a purified genome in 10 seconds.
4. Synthesizer — genome + mutagen base + catalyst → serum. The base is made with a bottle o' enchanting, so transformation costs experience. Harder species need more catalyst and more time; a genome of 85% purity gives two ampoules.
5. Inject — right-click once. What stays in your hand is the empty syringe: the needle is reused, the reagents are the cost.
6. Live with it — dose again, or stop and let it fade, or roll it back.

Everything the lab needs is made at the Bio Workbench, which has its own recipes and a list of them next to the grid: click one and its ingredients are laid out from your inventory.

🌳 The gene tree

Press G for a catalogue of every species you have sampled: the creature, its research, what each threshold unlocks and its genes — abilities in green, weaknesses in red. The genes stay hidden until you have read a quarter of the genome.

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🧫 The five stages

Stage	Progress	What happens
I. Infection	1–20%	Nothing visible. Particles, and the first passive trait
II. Manifestation	21–40%	Your skin takes the strain's colour. First ability, first weakness
III. Mutation	41–70%	Glowing eyes, the creature's head grows over yours, the body takes its size
IV. Domination	71–99%	More of the creature on your skeleton — arms, bones, body. Your skin still shows through
V. Full Form	100%	You are rendered as the creature itself. This stage does not decay

Every transition is an event: a sound, a screen flash, a line in chat, and a short withdrawal while the body rearranges itself.

Flesh and bone

Nothing is laid over you — your own model turns into the creature. From stage II the infection spreads from where the needle went in, bone by bone, and every bone it reaches slowly takes the shape of its counterpart in the creature's body: a skeleton's limbs thin down to bones, a creeper's legs shrink to stubs as the body sinks onto them, its arms wither away and its hind legs sprout from under you. The skin changes with the shape — patches of the creature's flesh with an inflamed edge, in a pattern that is yours alone, closing into the creature's hide as each bone finishes. Every new stage wrenches the body with convulsions, and from stage III it twitches on its own. By 100% you already have the creature's shape; the full form is the last step, not a swap. First person follows all of it.

The body changes with them. Hitbox width, height and eye height move towards the creature's own values — at full form a creeper is 1.7 blocks tall — and reach grows or shrinks: a zombie's long arms reach half a block further, a creeper has nothing to reach with.

Full form

At 100% the player model is replaced by the real model of the creature, drawn through the vanilla mob renderer. That means its own animations and render layers, with your armour and your held item on it. Your walk cycle, head turn, crouch, swim, sprint, hurt flashes and burning all carry across, and your name still floats above you on a server. In first person you get the creature's own arm — or no arm at all, if it never had one. Turn it off with fullFormRender if it clashes with another mod.

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⚗️ Strains in this build

Strain	Gives	Takes
Zombie	Undead strength, regeneration in darkness, immunity to Hunger, +4 health	Burns in sunlight, moves 15% slower. No sleep from III; from IV only meat and rot, and no fine work
Skeleton	Arrows hit 1.5× harder, poison and hunger do nothing	−4 health, blasts hurt 1.5× more, burns in sunlight. No sleep from III; from IV cannot eat and never heals naturally
Creeper	Immune to blasts, +12% speed	Panics near cats, −1 attack damage, 1.5× fire damage, sheds armour at stage V. Loses its hands: no off-hand from III; from IV only five belt slots, no tools, weapons or crafting; at V three slots and no building

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🎛️ Control

• Stabilizer — locks your current level so it stops decaying. Use it again to release the lock.
• Reversal serum — rolls you back 15% per dose, with nausea, weakness and damage. Milk does not cure a strain, and that is on purpose.
• /mutagen — status, list, dose, set, lock, clear, research. Permission level 2. Takes both mutagen:zombie and the short zombie. The honest path to stage V takes in-game days, so testing needs a shortcut; dose ignores research limits for the same reason.

⚙️ Config

config/mutagen.json:

Key	Default	Meaning
transformationSpeed	1.0	Multiplier for absorption and decay
doseStrength	20.0	Reserve added by one 100%-purity dose
humanityPenalties	true	The body refusing armour and the rest of the price
sunlightBurn	true	Undead strains burning in daylight
hud	true	The mutation indicator
fullFormRender	true	Replacing the player model at stage V
maxGenes	1	Genes the body can hold. Chimeras arrive in 0.5
knowledgeScope	world	world — research is shared; player — each player keeps their own
researchSpeed	1.0	Multiplier for research gained per sequencer run
doubleSerumPurity	85.0	Genome purity from which a synthesis gives two ampoules; 101 turns it off
hybridRender	true	The creature's parts on your body at stages III–IV
bodyMorph	true	Proportions and posture change with the infection
bodyMotion	true	Convulsions between stages and twitches from stage III
pehkuiIntegration	true	Use Pehkui for body size when it is installed

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🌍 Localization

Language	Code
English	en_us
Russian	ru_ru
Ukrainian	uk_ua
Polish	pl_pl
German	de_de
French	fr_fr
Spanish	es_es

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⚖️ License

Licensed under the MIT License.

• Modpacks: Free to include in any modpack.
• Source Code: Free to view, modify and distribute, provided the copyright notice and license text are kept.

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🐛 Bug Reports & Suggestions

Found a bug or have a feature idea?
Please open an issue on the GitHub Issues Page.