Type combinations introduced each generation(post Gen I)

Generation II:

1. Water/Electric
2. Psychic/Flying
3. Rock
4. Grass/Flying
5. Water/Ground
6. Dark
7. Dark/Flying
8. Normal/Psychic
9. Bug/Steel
10. Ground/Flying
11. Steel/Ground
12. Bug/Rock
13. Bug/Fighting
14. Fire/Rock
15. Ice/Ground
16. Water/Rock
17. Steel/Flying
18. Dark/Fire
19. Water/Dragon
20. Rock/Dark

Retcons: 

1. Electric/Steel

Generation III:

1. Fire/Fighting
2. Water/Grass
3. Grass/Dark
4. Bug/Water
5. Grass/Fighting
6. Bug/Ground
7. Bug/Ghost
8. Dark/Ghost
9. Steel
10. Steel/Rock
11. Fighting/Psychic
12. Water/Dark
13. Fire/Ground
14. Ground/Dragon
15. Rock/Psychic
16. Rock/Grass
17. Steel/Psychic
18. Dragon/Psychic
19. Ice

Generation IV:

1. Grass/Ground
2. Water/Steel
3. Normal/Water
4. Ghost/Flying
5. Poison/Dark
6. Fighting/Steel
7. Poison/Fighting
8. Grass/Ice
9. Ice/Ghost
10. Electric/Ghost
11. Steel/Dragon
12. Fire/Steel
13. Ghost/Dragon
14. Flying

Generation V:

1. Psychic/Fire
2. Ground/Dark
3. Dark/Fighting
4. Normal/Grass
5. Water/Ghost
6. Bug/Electric
7. Grass/Steel
8. Ghost/Fire
9. Ground/Electric
10. Ground/Ghost
11. Dark/Steel
12. Dark/Dragon
13. Bug/Fire
14. Rock/Fighting
15. Dragon/Fire
16. Dragon/Electric
17. Dragon/Ice
18. Normal/Fighting

Retcons:

1. Electric/Fire
2. Electric/Ice
3. Electric/Grass

Generation VI:

1. Normal/Ground
2. Fire/Normal
3. Steel/Ghost
4. Poison/Dragon
5. Electric/Normal
6. Rock/Dragon
7. Rock/Ice
8. Fighting/Flying
9. Electric/Fairy
10. Rock/Fairy
11. Ghost/Grass
12. Psychic/Ghost
13. Water/Fire

Retcons:

1. Fairy
2. Normal/Fairy
3. Psychic/Fairy
4. Fairy/Flying
5. Water/Fairy
6. Steel/Fairy
7. Grass/Fairy

Mega Evolutions:

1. Grass/Dragon
2. Dragon/Fairy

Generation VII:

1. Fighting/Ice
2. Bug/Fairy
3. Poison/Fire
4. Ghost/Fairy
5. Normal/Dragon
6. Dragon/Fighting
7. Rock/Poison
8. Fighting/Ghost

Regional Variants:

1. Dark/Normal
2. Electric/Psychic
3. Ice/Steel
4. Ice/Fairy
5. Rock/Electric

Generation VIII:

1. Ice/Bug
2. Bug/Psychic
3. Dark/Fairy
4. Electric/Poison
5. Electric/Dark

Regional Variants:

1. Poison/Fairy
2. Ice/Fire

DLC Regional Variants:

1. Poison/Psychic

Legends: Arceus:

Hisuian Regional Variants:

1. Normal/Ghost

Edit (01.01.2020): Added Sword and Shield additions.
Edit (20.06.2020): Added Galarian Slowbro's Poison/Psychic.

Edit (25.10.2021): Added Hisuian Zorua/Zoroark's Normal/Ghost.