The best passives for Gumoss depend on the job you give it. Gumoss is Paldeck #12, a Grass / Ground Pal with Planting 1 — the sets below are the community-consensus best-in-slot for each role it can fill.

LegendDemon GodMuscleheadSpirit Emperor
Legend, Demon God and Musclehead stack raw attack; Spirit Emperor adds 20% Grass damage on top.
ArtisanSeriousLuckyWork Slave
Maximum work speed. Work Slave trades attack a base worker never uses; swap for Nocturnal on day-sleepers if sanity drops.
SwiftRunnerNimbleLegend
Every movement-speed passive stacks; Legend adds 15% more plus combat stats.
A perfect Gumoss also wants 100/100/100 IVs (breeding averages the parents with a bonus, so high-IV Gumoss parents compound) and 4-star condensation — feeding it spare copies raises this Grass / Ground Pal's stats and every work suitability a full level. Craft-speed and attack souls from the Statue of Power stack on top. The planner routes these passives from pals you own; see how to breed Gumoss for parent combos.
Breed this Gumoss build from your save →