Moonblast is learned by 47 species by level and 2 by egg

Effect, in PokéAPI's words

“Has a chance to lower the target’s Special Attack by one stage.”

Who learns it

49 species in all, 8 of 9 games shown

Scarlet and Violet: 31 species

Species	Method	Level
Clefable	Level up	1
Vileplume	Level up	1
Bellossom	Level up	1
Whimsicott	Level up	1
Florges	Level up	5
Oddish	Level up	28
Gloom	Level up	32
Hoothoot	Level up	33
Popplio	Level up	33
Swablu	Level up	40
Flabébé	Level up	41
Noctowl	Level up	43
Clefairy	Level up	44
Altaria	Level up	44
Brionne	Level up	45
Floette	Level up	46
Gardevoir	Level up	49
Sylveon	Level up	50
Primarina	Level up	51
Carbink	Level up	55
Lunala	Level up	56
Iron Valiant	Level up	56
Cresselia	Level up	60
Enamorus	Level up	65
Zacian	Level up	66
Zamazenta	Level up	66
Fezandipiti	Level up	72
Diancie	Level up	77
Flutter Mane	Level up	84
Cutiefly	Egg
Ribombee	Egg

Legends Arceus: 11 species

Species	Method	Level
Phione	Level up	36
Manaphy	Level up	36
Clefairy	Level up	37
Clefable	Level up	37
Cleffa	Level up	37
Togepi	Level up	43
Togetic	Level up	43
Gardevoir	Level up	43
Togekiss	Level up	43
Cresselia	Level up	46
Enamorus	Level up	47

Brilliant Diamond and Shining Pearl: 13 species

Species	Method	Level
Clefable	Level up	1
Vileplume	Level up	1
Bellossom	Level up	1
Gardevoir	Level up	1
Lunatone	Level up	1
Oddish	Level up	28
Gloom	Level up	32
Hoothoot	Level up	33
Swablu	Level up	40
Noctowl	Level up	43
Clefairy	Level up	44
Altaria	Level up	44
Cresselia	Level up	60

Sword and Shield: 34 species

Species	Method	Level
Clefable	Level up	1
Vileplume	Level up	1
Bellossom	Level up	1
Gardevoir	Level up	1
Lunatone	Level up	1
Musharna	Level up	1
Whimsicott	Level up	1
Gourgeist	Level up	1
Oddish	Level up	28
Gloom	Level up	32
Hoothoot	Level up	33
Popplio	Level up	33
Spritzee	Level up	36
Aromatisse	Level up	36
Swablu	Level up	40
Munna	Level up	40
Morelull	Level up	40
Noctowl	Level up	43
Clefairy	Level up	44
Altaria	Level up	44
Brionne	Level up	45
Sylveon	Level up	50
Shiinotic	Level up	50
Primarina	Level up	51
Carbink	Level up	55
Lunala	Level up	56
Cresselia	Level up	60
Xerneas	Level up	60
Tapu Lele	Level up	60
Tapu Fini	Level up	60
Zacian	Level up	66
Zamazenta	Level up	66
Diancie	Level up	77
Cutiefly	Egg

Let's Go Pikachu and Let's Go Eevee: 4 species

Species	Method	Level
Muk	Level up	1
Clefairy	Level up	28
Oddish	Level up	30
Gloom	Level up	45

Ultra Sun and Ultra Moon: 28 species

Species	Method	Level
Gardevoir	Level up	1, 62
Lunatone	Level up	1
Florges	Level up	1
Tapu Fini	Level up	1
Spritzee	Level up	31
Aromatisse	Level up	31
Xerneas	Level up	35
Popplio	Level up	36
Sylveon	Level up	37
Morelull	Level up	39
Hoothoot	Level up	40
Flabébé	Level up	41
Brionne	Level up	42
Oddish	Level up	43
Primarina	Level up	44
Shiinotic	Level up	44
Clefairy	Level up	46
Swablu	Level up	46
Floette	Level up	46
Noctowl	Level up	47
Lunala	Level up	47
Whimsicott	Level up	50
Carbink	Level up	50
Diancie	Level up	50
Altaria	Level up	52
Tapu Lele	Level up	58
Cresselia	Level up	99
Cutiefly	Egg

Sun and Moon: 28 species

Species	Method	Level
Gardevoir	Level up	1, 62
Lunatone	Level up	1
Florges	Level up	1
Tapu Fini	Level up	1
Spritzee	Level up	31
Aromatisse	Level up	31
Xerneas	Level up	35
Popplio	Level up	36
Sylveon	Level up	37
Morelull	Level up	39
Hoothoot	Level up	40
Flabébé	Level up	41
Brionne	Level up	42
Oddish	Level up	43
Primarina	Level up	44
Shiinotic	Level up	44
Clefairy	Level up	46
Swablu	Level up	46
Floette	Level up	46
Noctowl	Level up	47
Lunala	Level up	47
Whimsicott	Level up	50
Carbink	Level up	50
Diancie	Level up	50
Altaria	Level up	52
Tapu Lele	Level up	58
Cresselia	Level up	99
Cutiefly	Egg

Omega Ruby and Alpha Sapphire: 17 species

Species	Method	Level
Gardevoir	Level up	1, 62
Lunatone	Level up	1
Florges	Level up	1
Spritzee	Level up	31
Aromatisse	Level up	31
Xerneas	Level up	35
Sylveon	Level up	37
Flabébé	Level up	41
Oddish	Level up	43
Clefairy	Level up	46
Swablu	Level up	46
Floette	Level up	46
Whimsicott	Level up	50
Carbink	Level up	50
Diancie	Level up	50
Altaria	Level up	52
Cresselia	Level up	99