Mutations in Catch a Monster are rare modifiers that attach to pets and stack their stats above the base values. Four mutations exist right now — Shiny, Huge, Bloodlit, and Fairy — and two of them only roll under specific weather. When more than one mutation affects the same stat, the bonuses multiply using a 1 + X formula rather than adding flat.
All mutation effects and drop rates
Each mutation modifies a different combination of stats. Shiny and Huge are the two "always-on" mutations, while Bloodlit and Fairy are weather-gated and roll at much higher rates during their respective events.
| Mutation | Effect | Base rate | Condition |
|---|---|---|---|
| Shiny | +10% Attack, +30% Crit Rate (Crit Damage fixed at 200%) | 0.01% | Any weather |
| Huge | +40% Attack, +40% HP | 0.001% | Any weather |
| Bloodlit | +10% Crit Rate, +100% Crit Damage | 0.5% during Bloodmoon | Bloodmoon weather only |
| Fairy | -25% Damage Taken, -20% Cooldowns | 0.5% during Dreamveil | Dreamveil weather only |
The base Shiny and Huge rates also shift while special weather is active. During Bloodmoon, Shiny climbs to 0.3%, Bloodlit sits at 0.5%, and Huge moves up to 0.013%. Dreamveil follows the same pattern, with Shiny at 0.3%, Fairy at 0.5%, and Huge at 0.013%.
How the stacking math works
Mutations apply multiplicatively to the same stat. If a pet somehow has both Shiny and Huge attached, the Attack bonus is not 10% + 40% = 50%. It is (1 + 0.10) × (1 + 0.40) = 1.54, or a 54% increase over the base value.
Shiny's Critical Damage is locked at 200%, which means stacking Bloodlit's +100% Crit Damage on a Shiny pet still respects the multiplicative rule on the Crit Damage line. Crit Rate from Shiny (+30%) and Bloodlit (+10%) also multiply rather than add.
Weather-gated mutations: Bloodmoon and Dreamveil
Bloodlit and Fairy do not exist outside their weather events. Bloodmoon and Dreamveil each have roughly a 0.02 chance to appear outside the normal day/night cycle, so both are genuinely rare environmental states.
When either weather triggers, Shiny and Huge rates also spike, which makes those windows the most efficient time to hatch eggs or catch wild monsters. If you are sitting on a stockpile of eggs, hold them until one of these weather events rolls.
Combining mutations on the same pet
Fusing two pets that each have a different mutation does not merge the mutations. A fuse between a Shiny C-rank and a Bloodlit C-rank produces either a B-rank Shiny or a B-rank Bloodlit, not a single pet carrying both.
To actually stack two mutations onto one pet, you need consumables. Mutation fruits and vials are the only way to apply a second mutation. The Blood Fruit, which grants the Bloodlit mutation, can be found at Dragon Breath Castle. The Shiny Vial is obtained by completing in-game tasks.
What each mutation is best for
Picking which mutation to chase depends on the pet's role. Shiny and Bloodlit are offensive — they push crit stats and damage output, which scales well on attackers used in Endless Spire and boss content. Huge is a brute-force buff that lifts both Attack and HP, useful for pets that need to survive while dealing damage.
Fairy is the only defensive/utility mutation. The 25% damage reduction and 20% cooldown cut make it strong on support pets or anchors in long fights where ability uptime matters more than raw damage numbers.
Confirming a mutation worked
Mutated pets show a visual indicator on their model and an icon next to their name in the inventory. If the stat sheet does not display the bonus listed in the table above, the mutation did not apply — restart the game once and check again before assuming the roll failed.
Fusing a mutated pet upgrades the rank while keeping the mutation attached, so a C-rank Shiny that becomes a B-rank Shiny is the expected outcome of a single-mutation fuse. Only the consumable fruits and vials can layer a second mutation on top.