Misty Terrain is learned by 18 species by level, 58 by machine and 5 by egg

Effect, in PokéAPI's words

“For five turns, protects all Pokémon on the ground from major status ailments and confusion, and halves the power of incoming Dragon moves.”

Who learns it

58 species in all, 7 games

Scarlet and Violet: 49 species

Species	Method	Level
Gardevoir	Level up, Machine	1
Florges	Level up, Machine	1
Popplio	Level up, Machine	27
Sylveon	Level up, Machine	35
Brionne	Level up, Machine	35
Flabébé	Level up, Machine	37
Primarina	Level up, Machine	37
Floette	Level up, Machine	43
Milcery	Level up, Machine	45
Alcremie	Level up, Machine	45
Meowstic	Level up, Machine	59
Clefairy	Machine
Clefable	Machine
Jigglypuff	Machine
Wigglytuff	Machine
Mew	Machine
Cleffa	Machine
Igglybuff	Machine
Marill	Machine
Azumarill	Machine
Ralts	Machine
Kirlia	Machine
Gallade	Machine
Arceus	Machine
Cottonee	Machine
Whimsicott	Machine
Alomomola	Machine
Dedenne	Machine
Carbink	Machine
Klefki	Machine
Volcanion	Machine
Mimikyu	Machine
Magearna	Machine
Hatenna	Machine
Hattrem	Machine
Hatterene	Machine
Impidimp	Machine
Morgrem	Machine
Grimmsnarl	Machine
Zacian	Machine
Enamorus	Machine
Quaxly	Machine
Quaxwell	Machine
Quaquaval	Machine
Fidough	Machine
Dachsbun	Machine
Scream Tail	Machine
Flutter Mane	Machine
Iron Valiant	Machine

Brilliant Diamond and Shining Pearl: 5 species

Species	Method	Level
Gardevoir	Level up	1
Cleffa	Egg
Igglybuff	Egg
Ralts	Egg
Mawile	Egg

Sword and Shield: 33 species

Species	Method	Level
Gardevoir	Level up, Machine	1
Mr. Rime	Level up, Machine	1
Spritzee	Level up, Machine	24
Aromatisse	Level up, Machine	24
Popplio	Level up, Machine	27
Sylveon	Level up, Machine	35
Brionne	Level up, Machine	35
Primarina	Level up, Machine	37
Xerneas	Level up, Machine	40
Milcery	Level up, Machine	45
Alcremie	Level up, Machine	45
Audino	Level up, Machine	56
Meowstic	Level up, Machine	59
Tapu Fini	Level up, Machine	75
Clefairy	Machine
Clefable	Machine
Jigglypuff	Machine
Wigglytuff	Machine
Mr. Mime	Machine
Mew	Machine
Cleffa	Machine
Igglybuff	Machine
Marill	Machine
Azumarill	Machine
Ralts	Machine
Kirlia	Machine
Mawile	Machine
Mime Jr.	Machine
Gallade	Machine
Cottonee	Machine
Whimsicott	Machine
Klefki	Machine
Volcanion	Machine

Ultra Sun and Ultra Moon: 20 species

Species	Method	Level
Mr. Mime	Level up	1
Gardevoir	Level up	1
Audino	Level up	1
Florges	Level up	1
Tapu Fini	Level up	1
Sylveon	Level up	29
Flabébé	Level up	37
Spritzee	Level up	42
Aromatisse	Level up	42
Floette	Level up	43
Popplio	Level up	46
Meowstic	Level up	50
Brionne	Level up	55
Primarina	Level up	60
Xerneas	Level up	63
Cleffa	Egg
Igglybuff	Egg
Ralts	Egg
Mawile	Egg
Cottonee	Egg

Sun and Moon: 19 species

Species	Method	Level
Mr. Mime	Level up	1
Gardevoir	Level up	1
Audino	Level up	1
Florges	Level up	1
Tapu Fini	Level up	1
Sylveon	Level up	29
Flabébé	Level up	37
Spritzee	Level up	42
Aromatisse	Level up	42
Floette	Level up	43
Popplio	Level up	46
Meowstic	Level up	50
Brionne	Level up	55
Primarina	Level up	60
Xerneas	Level up	63
Cleffa	Egg
Igglybuff	Egg
Ralts	Egg
Mawile	Egg

Omega Ruby and Alpha Sapphire: 15 species

Species	Method	Level
Mr. Mime	Level up	1
Gardevoir	Level up	1
Audino	Level up	1
Florges	Level up	1
Sylveon	Level up	29
Flabébé	Level up	37
Spritzee	Level up	42
Aromatisse	Level up	42
Floette	Level up	43
Meowstic	Level up	50
Xerneas	Level up	63
Cleffa	Egg
Igglybuff	Egg
Ralts	Egg
Mawile	Egg

X and Y: 14 species

Species	Method	Level
Mr. Mime	Level up	1
Gardevoir	Level up	1
Florges	Level up	1
Sylveon	Level up	29
Flabébé	Level up	37
Spritzee	Level up	42
Aromatisse	Level up	42
Floette	Level up	43
Meowstic	Level up	50
Xerneas	Level up	63
Cleffa	Egg
Igglybuff	Egg
Ralts	Egg
Mawile	Egg