Yes. In Palworld v1.0.3, Green Slime can get Ferocious through currently verified methods: it is in the standard random pool. Ferocious is in the standard random passive pool in v1.0.3, so it can appear on a caught or bred Green Slime and be inherited from parents that have it. The facts behind this answer are graded B and come from 2 registered sources.
Reason
Attack +20%
Rank
3
Random pool
Yes
Other Pals
299
Green Slime breeding recipes
1
Fixed passives on Green Slime
0
Custom slots available
4
Verified evidence claims behind this verdict
1
Green Slime parent pairs with a direct source of Ferocious
1 of 1
Ferocious breeding route for Green Slime: 1 of 1 parent pair include a direct source (Green Slime).
Why
Ferocious is in the standard random passive pool in v1.0.3, so it can appear on a caught or bred Green Slime and be inherited from parents that have it.
How Ferocious can be acquired on Green Slime in v1.0.3
Current method
Available for Green Slime?
Note
Fixed / innate
No
Green Slime is born with no fixed passive.
Random pool (catch or hatch)
Yes
Ferocious is in the standard random pool, so it can appear on a caught or hatched Green Slime.
Implant (Surgery Table)
No
Ferocious: no verified item method grants it here.
Breeding inheritance
Yes
Green Slime can inherit Ferocious along a verified breeding chain, under the standard passive-inheritance rule this dataset has not independently sourced.
Verdict per requested component on Green Slime in Palworld v1.0.3
Ferocious is in the standard random passive pool in v1.0.3, so it can appear on a caught or bred Green Slime and be inherited from parents that have it.
B B · 1 source
How it reaches this Pal
Ferocious is in the standard random pool, so it can appear on a caught or hatched Green Slime.
299 Pals obtain Ferocious directly in v1.0.3 (Demon Eye, Depresso, Digtoise, Dinossom and Dinossom Lux).
Green Slime breeds only from two Green Slime parents in v1.0.3, so no other species can bring Ferocious into its line.
5 of 299 shown
What you can do now
Ferocious is in the standard random pool, so it can appear on a caught or hatched Green Slime.
Alternative: Green Slime can inherit Ferocious along a verified breeding chain, under the standard passive-inheritance rule this dataset has not independently sourced.