~=type change due to introduction to Fairy-types
Gen 1:
Count: 37 (33 by Gen 1 Type Chart)
Normal/-, Normal/Flying, Normal/Fairy~(Normal/-), Fire/-, Fire/Flying, Water/-, Water/Ice, Water/Fighting, Water/Poison, Water/Flying, Water/Psychic, Electric/-, Electric/Flying, Electric/Steel~(Electric/-), Grass/-, Grass/Poison, Grass/Psychic, Ice/Flying, Ice/Psychic, Fighting/-, Poison/-, Poison/Ground, Poison/Flying, Ground/-, Psychic/-, Psychic/Fairy~(Psychic/-), Bug/-, Bug/Grass, Bug/Poison, Bug/Flying, Rock/Water, Rock/Ground, Rock/Flying, Ghost/Poison, Dragon/-, Dragon/Flying, and Fairy/-~(Normal/-)
Gen 2:
Count: 23 (21 by Gen 2-5 Type Chart)
Normal/Psychic, Fire/Rock, Water/Electric, Water/Ground, Water/Dragon, Water/Fairy~(Water/-), Grass/Flying, Ground/Flying, Ice/Ground, Psychic/Flying, Bug/Fighting, Bug/Rock, Bug/Steel, Rock/-, Rock/Dark, Ghost/-, Dark/-, Dark/Fire, Dark/Ice, Dark/Flying, Steel/Ground, Steel/Flying, and Fairy/Flying~(Normal/Flying)
Gen 3:
Count: 21 (20 by Gen 2-5 Type Chart)
Fire/Fighting, Fire/Ground, Water/Grass, Water/Dark, Grass/Fighting, Grass/Dark, Ice/-, Fighting/Psychic, Ground/Psychic, Ground/Dragon, Bug/Water, Bug/Ground, Bug/Ghost, Rock/Grass, Rock/Psychic, Dragon/Psychic, Dark/Ghost, Steel/-, Steel/Psychic, Steel/Rock, and Steel/Fairy~(Steel/-)
Gen 4:
Count: 16 (13 by Gen 2-5 Type Chart and Gen 4 games)
Normal/Water, Fire/Steel, Water/Steel
Electric/Ghost~(other new types through this Pokémon's forms include Electric/Fire, Electric/Grass, and Electric/Ice), Grass/Ice, Grass/Ground, Ice/Ghost, Fighting/Steel, Poison/Fighting, Poison/Dark, Ghost/Flying, Ghost/Dragon, and Steel/Dragon
Gen 5:
Count: 20 (19 by Gen 2-5 Type Chart)
Normal/Grass, Normal/Fighting, Water/Ghost, Grass/Steel, Grass/Fairy~(Grass/-), Ground/Electric, Ground/Ghost, Ground/Dark, Flying/-, Bug/Fire, Bug/Electric, Rock/Fighting, Ghost/Fire, Dragon/Fire, Dragon/Electric, Dragon/Ice, Dark/Fighting, Dark/Dragon, Dark/Steel, and Psychic/Fire
Gen 6:
Count: 16 (14 not including Megas)
Normal/Ground, Fire/Normal, Fire/Water, Electric/Normal, Electric/Fairy, Grass/Dragon(Mega), Fighting/Flying, Poison/Dragon, Psychic/Ghost, Rock/Ice, Rock/Dragon, Rock/Fairy, Ghost/Grass, Dragon/Fairy(Mega), Dark/Psychic, and Steel/Ghost
Gen: 7
Count: 13 (8 not including Alolan Forms)
Normal/Dragon, Electric/Psychic(A), Ice/Steel(A), Ice/Fairy(A), Fighting/Ice, Fighting/Ghost, Poison/Fire, Poison/Rock, Bug/Fairy, Rock/Electric(A), Ghost/Fairy, Dragon/Fighting, and Dark/Normal(A)
Gen: 8
Count: 9 (5 not including Galarian Forms and the 1 Hisuian Form)
Electric/Poison, Electric/Dark, Ice/Fire(G), Ice/Bug, Poison/Psychic(G), Poison/Fairy(G), Bug/Psychic, Dark/Fairy, and Normal/Ghost(H)
Gen: 9
Count: 7 (5 not including Paradoxes)
Bug/Dark, Electric/Fighting, Poison/Normal, Grass/Fire, Steel/Poison, Fighting/Ground(P), and Fighting/Fairy(P).
The remaining 9 dual-types can be found here.