Cross Poison is learned by 10 species by level, 26 by machine and 6 by egg

Effect, in PokéAPI's words

“Has an increased chance for a critical hit and a chance to poison the target.”

Who learns it

36 species in all, 8 of 13 games shown

Scarlet and Violet: 7 species

Species	Method	Level
Eternatus	Level up	32
Fezandipiti	Level up	32
Spinarak	Level up	44
Ariados	Level up	50
Gligar	Egg
Gliscor	Egg
Shroodle	Egg

Legends Arceus: 5 species

Species	Method	Level
Skorupi	Level up	18
Drapion	Level up	18
Zubat	Level up	25
Golbat	Level up	25
Crobat	Level up	25

Brilliant Diamond and Shining Pearl: 9 species

Species	Method	Level
Crobat	Level up	Evolve, 1
Parasect	Level up	1
Skorupi	Level up	39
Drapion	Level up	39
Spinarak	Level up	47
Ariados	Level up	55
Paras	Egg
Gligar	Egg
Anorith	Egg

Sword and Shield: 26 species

Species	Method	Level
Crobat	Level up, Machine	Evolve, 1
Eternatus	Level up, Machine	32
Skorupi	Level up, Machine	39
Drapion	Level up, Machine	39
Machamp	Machine
Tentacool	Machine
Tentacruel	Machine
Scyther	Machine
Kabutops	Machine
Mew	Machine
Scizor	Machine
Sceptile	Machine
Anorith	Machine
Armaldo	Machine
Vespiquen	Machine
Toxicroak	Machine
Scolipede	Machine
Garbodor	Machine
Joltik	Machine
Galvantula	Machine
Toxapex	Machine
Lurantis	Machine
Salazzle	Machine
Nihilego	Machine
Naganadel	Machine
Obstagoon	Machine

Ultra Sun and Ultra Moon: 10 species

Species	Method	Level
Crobat	Level up	Evolve, 1
Parasect	Level up	1
Spinarak	Level up	47
Skorupi	Level up	49
Ariados	Level up	55
Drapion	Level up	57
Paras	Egg
Gligar	Egg
Anorith	Egg
Joltik	Egg

Sun and Moon: 10 species

Species	Method	Level
Crobat	Level up	Evolve, 1
Parasect	Level up	1
Spinarak	Level up	47
Skorupi	Level up	49
Ariados	Level up	55
Drapion	Level up	57
Paras	Egg
Gligar	Egg
Anorith	Egg
Joltik	Egg

Omega Ruby and Alpha Sapphire: 10 species

Species	Method	Level
Parasect	Level up	1
Crobat	Level up	1
Spinarak	Level up	47
Skorupi	Level up	49
Ariados	Level up	55
Drapion	Level up	57
Paras	Egg
Gligar	Egg
Anorith	Egg
Joltik	Egg

X and Y: 10 species

Species	Method	Level
Parasect	Level up	1
Crobat	Level up	1
Spinarak	Level up	47
Skorupi	Level up	49
Ariados	Level up	55
Drapion	Level up	57
Paras	Egg
Gligar	Egg
Anorith	Egg
Joltik	Egg