Breeding System Guide
Breeding is one of the core pillars of Mewgenics. All the loot and experience your cats bring back from expeditions ultimately serves one goal: raising a stronger next generation.
Every time you End Day, cats in the same room may pair up and produce a kitten. This isn’t just random luck — the game runs a detailed inheritance calculation under the hood. Understanding it lets you dramatically improve your offspring quality.
House Stats: The Foundation of Breeding
Breeding quality is entirely driven by the furniture in your rooms. The game has 5 house stats, and each one directly affects breeding outcomes:
| Stat | Effect | Key Thresholds |
|---|---|---|
| Appeal | Increases stat quality and ability diversity of stray cats. Applies to the entire house. | 100+ guarantees strays have a 2nd active ability; 200+ guarantees a passive |
| Comfort | High comfort → cats are more likely to breed; low comfort → cats are more likely to fight | More than 4 cats per room reduces comfort by 1 per extra cat |
| Stimulation | The most important breeding stat! Affects the probability of inheriting higher stats and abilities | 32+ guarantees inheriting 1 active ability; 95+ guarantees a passive; 196+ guarantees 2 active abilities |
| Health | High health helps cats recover from injuries and disorders overnight; low health increases disorder risk | — |
| Mutation | Increases the chance for cats to develop mutations overnight | — |
Tip: Stimulation is the king stat for breeding — it affects both stat inheritance and ability inheritance. Prioritize stacking it early on; the returns far outweigh other stats.
How Kittens Are Born
Every kitten’s birth runs through 13 internal steps. Here are the ones that matter most:
Stat Inheritance
Kittens have 7 core stats, and each one is inherited from one parent. Higher Stimulation increases the chance of picking the higher value between the two parents:
- Stimulation 0 → 50% chance to pick the higher stat (pure coin flip)
- Stimulation 100 → ~67% chance to pick the higher stat
- Stimulation 200 → 75% chance to pick the higher stat
The same pair of strong cats will produce noticeably better kittens in a Stimulation 200 room compared to an empty one.
Ability Inheritance
Ability inheritance is split between active and passive, with probabilities driven by Stimulation:
- 1st Active Ability: Probability =
0.20 + 0.025 × Stimulation(guaranteed at Stimulation ≥ 32) - 2nd Active Ability: Probability =
0.02 + 0.005 × Stimulation(guaranteed at Stimulation ≥ 196) - Passive Ability: Probability =
0.05 + 0.01 × Stimulation(guaranteed at Stimulation ≥ 95)
If only one parent has class abilities, high Stimulation makes the system prefer that parent as the ability source.
Also, if either parent has Skill Share+ (the upgraded version of the passive), their other passive is guaranteed to pass to the kitten — an incredibly powerful breeding passive.
Disorder Inheritance
Kittens have a 15% chance of inheriting one random disorder from the mother, and an independent 15% chance from the father. This means a kitten might inherit 0, 1, or 2 disorders. This probability is not affected by furniture or Stimulation.
Body Part Inheritance
- 80% chance: All body parts are inherited from parents
- 20% chance: One random body part is regenerated; the rest are inherited normally
Each inherited part picks between the mother’s and father’s version. If only one parent’s version of that part is mutated, the system favors the mutated version (more so at higher Stimulation).
Symmetrical parts (legs, arms, eyes, eyebrows, ears) are mirrored after inheritance, so a bred kitten can have at most 10 mutations (body, head, tail, leg, arm, eye, eyebrow, ear, mouth, fur).
Inbreeding: Risk and Reward
When you finally breed a perfect cat, you’ll be tempted to pair it with relatives to “lock in the bloodline.” You can do it, but pace yourself carefully.
Every cat has an inbreeding coefficient (between 0 and 1):
- Stray cats always have a coefficient of 0
- Breeding between first cousins or closer raises the coefficient
- Breeding with cats more distant than first cousins lowers it
The higher the coefficient, the worse the consequences:
Birth-defect Disorders: When a kitten inherits fewer than 2 disorders from parents, the game rolls for a birth-defect disorder. Probability: 0.02 + 0.4 × max(coefficient - 0.2, 0). Even at low coefficients there’s a baseline 2% chance; at maximum it spikes to 42%.
Birth Defects: When the coefficient > 0.05, if random < coefficient × 1.5, the kitten receives defective body parts. At coefficient > 0.9, defect parts are applied in two passes — basically a write-off.
Practical Advice: An occasional backcross is fine — the coefficient rises slowly. But several consecutive generations of close-relative pairing will push it dangerously close to 1. Introducing stray cats (always coefficient 0) to dilute the bloodline is the sustainable long-term strategy.
Mutations
Mutations are triggered by the Mutation house stat — placing mutation-boosting furniture in a room gives cats a chance to mutate overnight. Mutations alter body parts and can bring both positive and negative effects.
An important property of mutations is that they’re inheritable: mutated body parts are favored by the inheritance system when breeding. If you roll a good mutation, you can pass it down through continued breeding.
Practical Breeding Strategies
- Stimulation is priority #1: 32+ guarantees ability inheritance, 95+ secures passives, 196+ locks in double actives.
- Keep Comfort positive: Otherwise cats fight instead of breeding. Though if you want cats to fight for permanent stat gains, you can intentionally lower it.
- One pair per room: More than 4 cats per room drops Comfort. Isolate your best breeders.
- Leverage stray cats: Higher Appeal brings stronger strays. Strays always have 0 inbreeding coefficient — the perfect “bloodline diluter.”
- Focus on base stats: Stats gained from leveling up don’t inherit. Only base stats pass to offspring. When picking breeders, look at the foundations, not the level-up screen.
- Watch for Skill Share+: This passive guarantees that the parent’s other passive transfers to the kitten — a must-have for serious breeding.
Happy with your kitten? Slap on a class collar, equip the best gear, and send it off to adventure in Boone County. Good luck!