Tickle is learned by 17 species by level and 57 by egg

Effect, in PokéAPI's words

“Lowers the target’s Attack and Defense by one stage.”

Who learns it

71 species in all, 8 of 17 games shown

Scarlet and Violet: 45 species

Species	Method	Level
Whiscash	Level up	1
Gothorita	Level up	1
Gothitelle	Level up	1
Dondozo	Level up	5
Wo-Chien	Level up	5
Gothita	Level up	8
Aipom	Level up	15
Ambipom	Level up	15
Minccino	Level up	36
Clefairy	Egg
Clefable	Egg
Oddish	Egg
Gloom	Egg
Vileplume	Egg
Bellsprout	Egg
Weepinbell	Egg
Victreebel	Egg
Tentacool	Egg
Tentacruel	Egg
Lapras	Egg
Eevee	Egg
Pichu	Egg
Cleffa	Egg
Bellossom	Egg
Lotad	Egg
Lombre	Egg
Ludicolo	Egg
Slakoth	Egg
Azurill	Egg
Feebas	Egg
Milotic	Egg
Turtwig	Egg
Grotle	Egg
Torterra	Egg
Finneon	Egg
Cottonee	Egg
Whimsicott	Egg
Cinccino	Egg
Alomomola	Egg
Espurr	Egg
Meowstic	Egg
Morpeko	Egg
Tandemaus	Egg
Toedscool	Egg
Finizen	Egg

Brilliant Diamond and Shining Pearl: 30 species

Species	Method	Level
Whiscash	Level up	1
Aipom	Level up	15
Ambipom	Level up	15
Tangela	Level up	44
Tangrowth	Level up	44
Oddish	Egg
Machop	Egg
Bellsprout	Egg
Tentacool	Egg
Krabby	Egg
Mr. Mime	Egg
Lapras	Egg
Eevee	Egg
Omanyte	Egg
Pichu	Egg
Cleffa	Egg
Marill	Egg
Zigzagoon	Egg
Lotad	Egg
Slakoth	Egg
Azurill	Egg
Skitty	Egg
Mawile	Egg
Wailmer	Egg
Lileep	Egg
Feebas	Egg
Turtwig	Egg
Cherubi	Egg
Mime Jr.	Egg
Finneon	Egg

Sword and Shield: 37 species

Species	Method	Level
Whiscash	Level up	1
Cinccino	Level up	1
Gothorita	Level up	1
Gothitelle	Level up	1
Gothita	Level up	8
Nihilego	Level up	10
Minccino	Level up	36
Tangela	Level up	44
Tangrowth	Level up	44
Tapu Lele	Level up	65
Oddish	Egg
Machop	Egg
Tentacool	Egg
Mr. Mime	Egg
Lapras	Egg
Eevee	Egg
Omanyte	Egg
Pichu	Egg
Cleffa	Egg
Marill	Egg
Zigzagoon	Egg
Lotad	Egg
Azurill	Egg
Mawile	Egg
Wailmer	Egg
Lileep	Egg
Feebas	Egg
Cherubi	Egg
Mime Jr.	Egg
Cottonee	Egg
Emolga	Egg
Heatmor	Egg
Espurr	Egg
Pyukumuku	Egg
Togedemaru	Egg
Drampa	Egg
Morpeko	Egg

Ultra Sun and Ultra Moon: 46 species

Species	Method	Level
Whiscash	Level up	1
Mime Jr.	Level up	1
Cinccino	Level up	1
Gothorita	Level up	1, 7
Gothitelle	Level up	1, 7
Nihilego	Level up	1
Gothita	Level up	7
Minccino	Level up	9
Aipom	Level up	15
Ambipom	Level up	15
Tapu Lele	Level up	38
Omanyte	Level up	43
Tangela	Level up	44
Tangrowth	Level up	46
Omastar	Level up	48
Oddish	Egg
Machop	Egg
Bellsprout	Egg
Tentacool	Egg
Krabby	Egg
Lapras	Egg
Eevee	Egg
Pichu	Egg
Cleffa	Egg
Zigzagoon	Egg
Lotad	Egg
Slakoth	Egg
Azurill	Egg
Skitty	Egg
Mawile	Egg
Wailmer	Egg
Lileep	Egg
Feebas	Egg
Turtwig	Egg
Cherubi	Egg
Finneon	Egg
Pansage	Egg
Pansear	Egg
Panpour	Egg
Cottonee	Egg
Emolga	Egg
Alomomola	Egg
Heatmor	Egg
Binacle	Egg
Pyukumuku	Egg
Togedemaru	Egg

Sun and Moon: 46 species

Species	Method	Level
Whiscash	Level up	1
Mime Jr.	Level up	1
Cinccino	Level up	1
Gothorita	Level up	1, 7
Gothitelle	Level up	1, 7
Nihilego	Level up	1
Gothita	Level up	7
Minccino	Level up	9
Aipom	Level up	15
Ambipom	Level up	15
Tapu Lele	Level up	38
Omanyte	Level up	43
Tangela	Level up	44
Tangrowth	Level up	46
Omastar	Level up	48
Oddish	Egg
Machop	Egg
Bellsprout	Egg
Tentacool	Egg
Krabby	Egg
Lapras	Egg
Eevee	Egg
Pichu	Egg
Cleffa	Egg
Zigzagoon	Egg
Lotad	Egg
Slakoth	Egg
Azurill	Egg
Skitty	Egg
Mawile	Egg
Wailmer	Egg
Lileep	Egg
Feebas	Egg
Turtwig	Egg
Cherubi	Egg
Finneon	Egg
Pansage	Egg
Pansear	Egg
Panpour	Egg
Cottonee	Egg
Emolga	Egg
Alomomola	Egg
Heatmor	Egg
Binacle	Egg
Pyukumuku	Egg
Togedemaru	Egg

Omega Ruby and Alpha Sapphire: 42 species

Species	Method	Level
Whiscash	Level up	1
Mime Jr.	Level up	1
Cinccino	Level up	1
Gothorita	Level up	1, 7
Gothitelle	Level up	1, 7
Gothita	Level up	7
Minccino	Level up	9
Aipom	Level up	15
Ambipom	Level up	15
Omanyte	Level up	43
Tangela	Level up	44
Tangrowth	Level up	46
Omastar	Level up	48
Oddish	Egg
Machop	Egg
Bellsprout	Egg
Tentacool	Egg
Krabby	Egg
Lapras	Egg
Eevee	Egg
Pichu	Egg
Cleffa	Egg
Zigzagoon	Egg
Lotad	Egg
Slakoth	Egg
Azurill	Egg
Skitty	Egg
Mawile	Egg
Wailmer	Egg
Lileep	Egg
Feebas	Egg
Turtwig	Egg
Cherubi	Egg
Finneon	Egg
Pansage	Egg
Pansear	Egg
Panpour	Egg
Cottonee	Egg
Emolga	Egg
Alomomola	Egg
Heatmor	Egg
Binacle	Egg

X and Y: 42 species

Species	Method	Level
Whiscash	Level up	1
Mime Jr.	Level up	1
Cinccino	Level up	1
Gothorita	Level up	1, 7
Gothitelle	Level up	1, 7
Gothita	Level up	7
Minccino	Level up	9
Aipom	Level up	15
Ambipom	Level up	15
Omanyte	Level up	43
Tangela	Level up	44
Tangrowth	Level up	46
Omastar	Level up	48
Oddish	Egg
Machop	Egg
Bellsprout	Egg
Tentacool	Egg
Krabby	Egg
Lapras	Egg
Eevee	Egg
Pichu	Egg
Cleffa	Egg
Zigzagoon	Egg
Lotad	Egg
Slakoth	Egg
Azurill	Egg
Skitty	Egg
Mawile	Egg
Wailmer	Egg
Lileep	Egg
Feebas	Egg
Turtwig	Egg
Cherubi	Egg
Finneon	Egg
Pansage	Egg
Pansear	Egg
Panpour	Egg
Cottonee	Egg
Emolga	Egg
Alomomola	Egg
Heatmor	Egg
Binacle	Egg

Black 2 and White 2: 41 species

Species	Method	Level
Whiscash	Level up	1
Mime Jr.	Level up	1
Cinccino	Level up	1
Gothorita	Level up	1, 7
Gothitelle	Level up	1, 7
Gothita	Level up	7
Minccino	Level up	9
Aipom	Level up	15
Ambipom	Level up	15
Omanyte	Level up	43
Tangela	Level up	46
Tangrowth	Level up	46
Omastar	Level up	48
Oddish	Egg
Machop	Egg
Bellsprout	Egg
Tentacool	Egg
Krabby	Egg
Lapras	Egg
Eevee	Egg
Pichu	Egg
Cleffa	Egg
Zigzagoon	Egg
Lotad	Egg
Slakoth	Egg
Azurill	Egg
Skitty	Egg
Mawile	Egg
Wailmer	Egg
Lileep	Egg
Feebas	Egg
Turtwig	Egg
Cherubi	Egg
Finneon	Egg
Pansage	Egg
Pansear	Egg
Panpour	Egg
Cottonee	Egg
Emolga	Egg
Alomomola	Egg
Heatmor	Egg