Yes. In Palworld v1.0.3, Selyne 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 Selyne 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
Selyne breeding recipes
1
Fixed passives on Selyne
0
Custom slots available
4
Verified evidence claims behind this verdict
1
Selyne parent pairs with a direct source of Ferocious
1 of 1
Ferocious breeding route for Selyne: 1 of 1 parent pair include a direct source (Selyne).
Why
Ferocious is in the standard random passive pool in v1.0.3, so it can appear on a caught or bred Selyne and be inherited from parents that have it.
How Ferocious can be acquired on Selyne in v1.0.3
Current method
Available for Selyne?
Note
Fixed / innate
No
Selyne 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 Selyne.
Implant (Surgery Table)
No
Ferocious: no verified item method grants it here.
Breeding inheritance
Yes
Selyne 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 Selyne 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 Selyne 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 Selyne.
299 Pals obtain Ferocious directly in v1.0.3 (Demon Eye, Depresso, Digtoise, Dinossom and Dinossom Lux).
Selyne breeds only from two Selyne 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 Selyne.
Alternative: Selyne can inherit Ferocious along a verified breeding chain, under the standard passive-inheritance rule this dataset has not independently sourced.