Hatch mutations roll when an egg opens; weather traits arrive during server weather. Current gameplay sources report that one hatch mutation and one weather trait can sit on the same pet. Keep intended pets or eggs in the pen—or ride the intended pet—because inventory pets are reported as ineligible for weather mutation.
Official boundary: Roblox lists the MUTATIONS event from Sep 19 at 14:00 UTC through Sep 26 at 14:00 UTC and says mutations “can be stacked with weather traits.” The names, multipliers, reported five-minute window and eligibility rules below come from current recorded-gameplay/community sources, not a developer-authored changelog.
Hatch mutations
These roll when an egg hatches. Current source tables report the tier multipliers below; read the live pet card afterward to see which displayed stats changed on your pet.
Weather mutations
These are tied to named weather events. Current sources report that map eggs, pen eggs, pen pets and the pet you are riding can be affected; inventory pets cannot.
Before, during and after a weather event
- Choose a keeper.Start with a pet already useful for travel or income; a large multiplier cannot fix the wrong underlying role.
- Make it eligible.Place the pet or egg in the pen, or keep the intended pet mounted. Do not leave the target in inventory.
- Use the window.Current guides report roughly five minutes. Keep running the normal loop while eligible targets remain out.
- Read the result.After the event, check the label and the final speed, cash-per-second and sale displays before changing your lineup.
What “stacking” does—and does not—mean
Hatch + weatherReported to coexist on one pet; this compatibility is the part the official event text supports.
Two hatch mutationsNot reported to stack. A pet carries one hatch layer.
Two weather traitsNot reported to stack. A stronger weather trait can replace a weaker one; weaker weather is reported not to downgrade a stronger trait.
Rebirth or calculation orderNot established by the event text. Do not assume additive or multiplicative order, a cap, odds, or that mutations survive a reset.
Fast troubleshooting
- No change after the event: confirm the target was in the pen or mounted rather than stored in inventory; eligibility gives a chance, not a guarantee.
- A high multiplier still feels weak: compare the final card, because the underlying pet can still be worse for your chosen job.
- A label changed: reread every displayed stat before selling, placing or riding the pet.
- Preparing to rebirth: read the live reset panel; current mutation sources do not establish what survives.