Tri Attack is learned by 20 species by level, 48 by machine and 1 by egg

Effect, in PokéAPI's words

“Has a chance to burn, freeze, or paralyze the target.”

Who learns it

52 species in all, 8 of 25 games shown

Scarlet and Violet: 12 species

Species	Method	Level
Magneton	Level up	Evolve
Dodrio	Level up	Evolve
Probopass	Level up	Evolve
Dugtrio	Level up	1
Magnezone	Level up	1
Hydreigon	Level up	1
Iron Jugulis	Level up	1
Terapagos	Level up	1
Sandy Shocks	Level up	28
Porygon	Level up	45
Porygon2	Level up	45
Porygon-Z	Level up	45

Legends Arceus: 8 species

Species	Method	Level
Porygon	Level up	21
Porygon-Z	Level up	21
Magneton	Level up	25
Magnezone	Level up	25
Uxie	Level up	32
Mesprit	Level up	32
Azelf	Level up	32
Probopass	Level up	34

Brilliant Diamond and Shining Pearl: 10 species

Species	Method	Level
Magneton	Level up	Evolve, 1
Dodrio	Level up	Evolve, 1
Probopass	Level up	Evolve, 1
Dugtrio	Level up	1
Magnezone	Level up	1
Togekiss	Level up	1
Porygon	Level up	45
Porygon2	Level up	45
Porygon-Z	Level up	45
Spearow	Egg

Sword and Shield: 42 species

Species	Method	Level
Magneton	Level up, Machine	Evolve, 1
Dugtrio	Level up, Machine	1
Magnezone	Level up, Machine	1
Togekiss	Level up, Machine	1
Hydreigon	Level up, Machine	1
Type: Null	Level up, Machine	35
Silvally	Level up, Machine	35
Porygon	Level up, Machine	45
Porygon2	Level up, Machine	45
Porygon-Z	Level up, Machine	45
Clefairy	Machine
Clefable	Machine
Jigglypuff	Machine
Wigglytuff	Machine
Abra	Machine
Kadabra	Machine
Alakazam	Machine
Slowpoke	Machine
Slowbro	Machine
Shellder	Machine
Cloyster	Machine
Chansey	Machine
Staryu	Machine
Starmie	Machine
Mewtwo	Machine
Mew	Machine
Togepi	Machine
Togetic	Machine
Slowking	Machine
Blissey	Machine
Latias	Machine
Latios	Machine
Uxie	Machine
Mesprit	Machine
Azelf	Machine
Beheeyem	Machine
Genesect	Machine
Magearna	Machine
Alcremie	Machine
Indeedee	Machine
Dragapult	Machine
Calyrex	Machine

Let's Go Pikachu and Let's Go Eevee: 24 species

Species	Method	Level
Dugtrio	Level up, Machine	Evolve, 1
Magneton	Level up, Machine	Evolve, 1
Dodrio	Level up, Machine	Evolve, 1
Porygon	Level up, Machine	22
Spearow	Machine
Fearow	Machine
Clefairy	Machine
Clefable	Machine
Jigglypuff	Machine
Wigglytuff	Machine
Abra	Machine
Kadabra	Machine
Alakazam	Machine
Slowpoke	Machine
Slowbro	Machine
Shellder	Machine
Cloyster	Machine
Drowzee	Machine
Hypno	Machine
Chansey	Machine
Staryu	Machine
Starmie	Machine
Mewtwo	Machine
Mew	Machine

Ultra Sun and Ultra Moon: 13 species

Species	Method	Level
Magneton	Level up	Evolve, 1
Dodrio	Level up	Evolve, 1
Probopass	Level up	Evolve, 1
Dugtrio	Level up	1
Magnezone	Level up	1
Hydreigon	Level up	1
Genesect	Level up	44
Porygon	Level up	50
Porygon2	Level up	50
Porygon-Z	Level up	50
Type: Null	Level up	75
Silvally	Level up	75
Spearow	Egg

Sun and Moon: 13 species

Species	Method	Level
Magneton	Level up	Evolve, 1
Dodrio	Level up	Evolve, 1
Probopass	Level up	Evolve, 1
Dugtrio	Level up	1
Magnezone	Level up	1
Hydreigon	Level up	1
Genesect	Level up	44
Porygon	Level up	50
Porygon2	Level up	50
Porygon-Z	Level up	50
Type: Null	Level up	75
Silvally	Level up	75
Spearow	Egg

Omega Ruby and Alpha Sapphire: 9 species

Species	Method	Level
Dugtrio	Level up	1
Hydreigon	Level up	1
Dodrio	Level up	25
Magneton	Level up	30
Genesect	Level up	44
Porygon	Level up	50
Porygon2	Level up	50
Porygon-Z	Level up	50
Spearow	Egg

Changed over time

One change since Generation I

1. Through Gen IEffect chance 0%20% from Gold and Silver, Generation II