The best passives for Green Slime depend on the job you give it. Green Slime is Paldeck #10002, a Grass Pal with Transporting 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 Green Slime also wants 100/100/100 IVs (breeding averages the parents with a bonus, so high-IV Green Slime parents compound) and 4-star condensation — feeding it spare copies raises this Grass 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 Green Slime for parent combos.
Breed this Green Slime build from your save →