Final Gambit is learned by 14 species by level and 9 by egg

Effect, in PokéAPI's words

“Inflicts damage equal to the user’s remaining HP. User faints.”

Who learns it

23 species in all, 8 of 9 games shown

Scarlet and Violet: 15 species

Species	Method	Level
Lucario	Level up	1
Basculin	Level up	40
Starly	Level up	41
Mankey	Level up	48
Staravia	Level up	48
Riolu	Level up	52
Veluza	Level up	55
Primeape	Level up	57
Staraptor	Level up	57
Annihilape	Level up	57
Diglett	Egg
Zangoose	Egg
Seviper	Egg
Squawkabilly	Egg
Wiglett	Egg

Brilliant Diamond and Shining Pearl: 14 species

Species	Method	Level
Primeape	Level up	1, 57
Lucario	Level up	1
Starly	Level up	41
Staravia	Level up	48
Mankey	Level up	50
Riolu	Level up	52
Staraptor	Level up	57
Rattata	Egg
Diglett	Egg
Farfetch’d	Egg
Shuckle	Egg
Nincada	Egg
Zangoose	Egg
Seviper	Egg

Sword and Shield: 11 species

Species	Method	Level
Lucario	Level up	1
Basculin	Level up	40
Shelmet	Level up	48
Accelgor	Level up	48
Riolu	Level up	52
Sirfetch’d	Level up	60
Victini	Level up	91
Diglett	Egg
Farfetch’d	Egg
Shuckle	Egg
Nincada	Egg

Ultra Sun and Ultra Moon: 17 species

Species	Method	Level
Primeape	Level up	1, 57
Accelgor	Level up	1, 56
Basculin	Level up	38
Starly	Level up	41
Staravia	Level up	48
Mankey	Level up	50
Riolu	Level up	50
Shelmet	Level up	56
Staraptor	Level up	57
Victini	Level up	81
Rattata	Egg
Diglett	Egg
Farfetch’d	Egg
Shuckle	Egg
Nincada	Egg
Zangoose	Egg
Seviper	Egg

Sun and Moon: 16 species

Species	Method	Level
Primeape	Level up	1, 57
Accelgor	Level up	1, 56
Basculin	Level up	38
Starly	Level up	41
Staravia	Level up	48
Mankey	Level up	50
Riolu	Level up	50
Shelmet	Level up	56
Staraptor	Level up	57
Victini	Level up	81
Rattata	Egg
Diglett	Egg
Shuckle	Egg
Nincada	Egg
Zangoose	Egg
Seviper	Egg

Omega Ruby and Alpha Sapphire: 16 species

Species	Method	Level
Primeape	Level up	1, 63
Accelgor	Level up	1, 56
Starly	Level up	41
Staravia	Level up	48
Riolu	Level up	50
Basculin	Level up	50
Mankey	Level up	53
Shelmet	Level up	56
Staraptor	Level up	57
Victini	Level up	81
Rattata	Egg
Diglett	Egg
Shuckle	Egg
Nincada	Egg
Zangoose	Egg
Seviper	Egg

X and Y: 16 species

Species	Method	Level
Primeape	Level up	1, 63
Accelgor	Level up	1, 56
Starly	Level up	41
Staravia	Level up	48
Riolu	Level up	50
Basculin	Level up	50
Mankey	Level up	53
Shelmet	Level up	56
Staraptor	Level up	57
Victini	Level up	81
Rattata	Egg
Diglett	Egg
Shuckle	Egg
Nincada	Egg
Zangoose	Egg
Seviper	Egg

Black 2 and White 2: 16 species

Species	Method	Level
Starly	Level up	41
Staravia	Level up	48
Basculin	Level up	51
Mankey	Level up	53
Riolu	Level up	55
Shelmet	Level up	56
Accelgor	Level up	56
Staraptor	Level up	57
Primeape	Level up	63
Victini	Level up	81
Rattata	Egg
Diglett	Egg
Shuckle	Egg
Nincada	Egg
Zangoose	Egg
Seviper	Egg