Leech Life is learned by 33 species by level, 73 by machine and 2 by egg

Effect, in PokéAPI's words

“Drains half the damage inflicted to heal the user.”

Who learns it

75 species in all, 8 of 25 games shown

Scarlet and Violet: 49 species

Species	Method	Level
Venonat	Level up, Machine	35
Larvesta	Level up, Machine	36
Volcarona	Level up, Machine	36
Venomoth	Level up, Machine	37
Dewpider	Level up, Machine	44
Araquanid	Level up, Machine	56
Slither Wing	Level up, Machine	84
Ekans	Machine
Arbok	Machine
Sandshrew	Machine
Sandslash	Machine
Bellsprout	Machine
Weepinbell	Machine
Victreebel	Machine
Mew	Machine
Spinarak	Machine
Ariados	Machine
Yanma	Machine
Surskit	Machine
Masquerain	Machine
Duskull	Machine
Dusclops	Machine
Kricketune	Machine
Yanmega	Machine
Dusknoir	Machine
Joltik	Machine
Galvantula	Machine
Noibat	Machine
Noivern	Machine
Litten	Machine
Torracat	Machine
Incineroar	Machine
Cutiefly	Machine
Ribombee	Machine
Fomantis	Machine
Lurantis	Machine
Salandit	Machine
Salazzle	Machine
Mimikyu	Machine
Impidimp	Machine
Morgrem	Machine
Grimmsnarl	Machine
Frosmoth	Machine
Tarountula	Machine
Spidops	Machine
Nymble	Machine
Lokix	Machine
Rellor	Machine
Rabsca	Machine

Legends Arceus: 6 species

Species	Method	Level
Duskull	Level up	18
Dusclops	Level up	18
Dusknoir	Level up	18
Zubat	Level up	43
Golbat	Level up	43
Crobat	Level up	43

Brilliant Diamond and Shining Pearl: 13 species

Species	Method	Level
Beautifly	Level up	25
Dustox	Level up	25
Spinarak	Level up	29
Ariados	Level up	32
Venonat	Level up	35
Venomoth	Level up	37
Kabuto	Level up	45
Kabutops	Level up	49
Zubat	Level up	55
Golbat	Level up	69
Crobat	Level up	69
Bellsprout	Egg
Yanma	Egg

Sword and Shield: 47 species

Species	Method	Level
Larvesta	Level up, Machine	36
Volcarona	Level up, Machine	36
Dewpider	Level up, Machine	44
Kabuto	Level up, Machine	45
Kabutops	Level up, Machine	49
Zubat	Level up, Machine	55
Araquanid	Level up, Machine	56
Golbat	Level up, Machine	69
Crobat	Level up, Machine	69
Sandshrew	Machine
Sandslash	Machine
Mew	Machine
Nincada	Machine
Ninjask	Machine
Shedinja	Machine
Drapion	Machine
Joltik	Machine
Galvantula	Machine
Shelmet	Machine
Accelgor	Machine
Genesect	Machine
Noibat	Machine
Noivern	Machine
Litten	Machine
Torracat	Machine
Incineroar	Machine
Cutiefly	Machine
Ribombee	Machine
Fomantis	Machine
Lurantis	Machine
Salandit	Machine
Salazzle	Machine
Wimpod	Machine
Golisopod	Machine
Mimikyu	Machine
Buzzwole	Machine
Naganadel	Machine
Dottler	Machine
Orbeetle	Machine
Sizzlipede	Machine
Centiskorch	Machine
Impidimp	Machine
Morgrem	Machine
Grimmsnarl	Machine
Cursola	Machine
Frosmoth	Machine
Dracovish	Machine

Let's Go Pikachu and Let's Go Eevee: 9 species

Species	Method	Level
Victreebel	Level up	1
Paras	Level up	23
Parasect	Level up	23
Zubat	Level up	25
Venonat	Level up	28
Venomoth	Level up	28
Golbat	Level up	31
Kabuto	Level up	48
Kabutops	Level up	54

Ultra Sun and Ultra Moon: 41 species

Species	Method	Level
Dewpider	Level up, Machine	29
Buzzwole	Level up, Machine	29
Zubat	Level up, Machine	31
Araquanid	Level up, Machine	33
Golbat	Level up, Machine	35
Venonat	Level up, Machine	35
Crobat	Level up, Machine	35
Venomoth	Level up, Machine	37
Paras	Machine
Parasect	Machine
Bellsprout	Egg
Mew	Machine
Spinarak	Machine
Ariados	Machine
Yanma	Egg
Nincada	Machine
Ninjask	Machine
Shedinja	Machine
Kricketune	Machine
Yanmega	Machine
Joltik	Machine
Galvantula	Machine
Shelmet	Machine
Accelgor	Machine
Larvesta	Machine
Volcarona	Machine
Noibat	Machine
Noivern	Machine
Litten	Machine
Torracat	Machine
Incineroar	Machine
Cutiefly	Machine
Ribombee	Machine
Fomantis	Machine
Lurantis	Machine
Salandit	Machine
Salazzle	Machine
Wimpod	Machine
Golisopod	Machine
Mimikyu	Machine
Naganadel	Machine

Sun and Moon: 40 species

Species	Method	Level
Dewpider	Level up, Machine	29
Buzzwole	Level up, Machine	29
Zubat	Level up, Machine	31
Araquanid	Level up, Machine	33
Golbat	Level up, Machine	35
Venonat	Level up, Machine	35
Crobat	Level up, Machine	35
Venomoth	Level up, Machine	37
Paras	Machine
Parasect	Machine
Bellsprout	Egg
Mew	Machine
Spinarak	Machine
Ariados	Machine
Yanma	Egg
Nincada	Machine
Ninjask	Machine
Shedinja	Machine
Kricketune	Machine
Yanmega	Machine
Joltik	Machine
Galvantula	Machine
Shelmet	Machine
Accelgor	Machine
Larvesta	Machine
Volcarona	Machine
Noibat	Machine
Noivern	Machine
Litten	Machine
Torracat	Machine
Incineroar	Machine
Cutiefly	Machine
Ribombee	Machine
Fomantis	Machine
Lurantis	Machine
Salandit	Machine
Salazzle	Machine
Wimpod	Machine
Golisopod	Machine
Mimikyu	Machine

Omega Ruby and Alpha Sapphire: 23 species

Species	Method	Level
Zubat	Level up	1
Golbat	Level up	1
Parasect	Level up	1, 11
Crobat	Level up	1
Ninjask	Level up	1, 5
Joltik	Level up	1
Galvantula	Level up	1
Shelmet	Level up	1
Accelgor	Level up	1
Volcarona	Level up	1, 10
Nincada	Level up	5
Shedinja	Level up	5
Noibat	Level up	5
Noivern	Level up	5
Larvesta	Level up	10
Paras	Level up	11
Spinarak	Level up	12
Ariados	Level up	12
Kricketune	Level up	14
Venonat	Level up	17
Venomoth	Level up	17
Bellsprout	Egg
Yanma	Egg

Changed over time

2 changes since Generation I

1. Through Gen VIPower 2080 from Sun and Moon, Generation VII
2. Through Gen VIPP 1510 from Sun and Moon, Generation VII