This was really hard.
1. Coin
2. Magikoopa/Kamek
3. Bob-omb
4. Bowser Jr without Clown Cart
5. Luigi Kart
6. Peach Kart
7. King Boo
8. Viruses
9. Cappy
10. Meowser
11. Dixie Kong
12. Cranky Kong
13. Poochy
14. Fawful
15. Jimmy T
16. Pyoro
17. Magikarp
18. Grookey
19. Scorbunny
20. Sobble
21. Octorok
22. Impa
23. Waddle Dee
24. Bandana Waddle Dee
25. Robobot Armor
26. Landmaster
27. Duck
28. Hector
29. Smick
30. Yuka/Rhythm Girl
31. Chorus Kids
32. Blue Falcon
33. Rex
34. Tamagon
35. Sami
36. Andy
37. Prince of Sable
39. Muddy Mole
40. Isaac
41. Dillon
42. Master Hand
43. Amelia N
44. N64 Logo
45. Wii Remote
Shorten this list for a generic Nintendo enemy traditional fighting game down to 20 (Goomba and Koopa Troopa automatically included, third party enemies are guest characters, so don't overdo them)
1. Shy Guy (Mario)
2. Boo (Mario)
3. Lakitu (Mario)
4. Hammer Bro (Mario)
5. Bob-Omb (Mario)
6. Kritter (Donkey Kong)
7. Zinger (Donkey Kong)
8. Klobber (Donkey Kong)
9. Octorok (Zelda)
10. Bokoblin (Zelda)
11. ReDead (Zelda)
12. Darknut (Zelda)
13. Metroid (Metroid)
14. Zebesian (Metroid)
15. E.M.M.I (Metroid)
16. Bandit (Yoshi)
17. Burt (Yoshi)
18. Toady (Yoshi)
19. Polar Bear (Ice Climbers)
20. Waddle Dee (Kirby)
21. Waddle Doo (Kirby)
22. Poppy Bros Jr. (Kirby)
23. Sharpclaw (Star Fox)
24. Gastly (Pokémon)
25. Koffing (Pokémon)
26. Starman (EarthBound)
27. Spiteful Crow (EarthBound)
28. Pigmask (Mother 3)
29. Risen (Fire Emblem)
30. Faceless (Fire Emblem)
31. Skuttler (Kid Icarus)
32. Eggplant Wizard (Kid Icarus)
33. Wario Nose (Wario)
34. Bulborb (Pikmin)
35. Octotrooper (Splatoon)
36. Salmanoid (Splatoon)
37. Motobug (Sonic)
38. Egg Pawn (Sonic)
39. Mettaur (Mega Man)
40. Serv-Bot (Mega Man)
41. Cactuar (Final Fantasy)
42. Tonberry (Final Fantasy)
43. Affinity (Bayonetta)
44. Mummy (Castlevania)
45. Jack Frost (Shin Megami Tensei/Persona)
46. Slime (Dragon Quest)
47. Gruntling (Banjo and Kazooie)
48. Creeper (Minecraft)
49. Mokujin (Tekken)
50. Shadow (Kingdom Hearts)