Android 16:Beat Android 16 with Goku.
Android 17: Beat Android 17 with Piccolo.
Android 18: Beat Android 18 with Krillen.
Android 20: Beat Android 20 with Goku.
Cell: Beat Cell with Goku.
Dabura: Get a certain amount of Kili on Babidi's Spaceship (I forget how much).
Majin, Super, and Kid buu: Also get a certain amount of kili on Babidi's Spaceship (I don't remember this either but it is higher than Dabura's).
Frieza: Beat Frieza with Goku
Future Trunks: Beat Vegeta on Namek with Kid Trunks.
Ginyu: Beat Ginyu on Namek with Vegeta.
Hercule: Beat Fat Buu with Great Saiyaman on stage 6.
Kabitoshin: Get 7 dragonballs and wish for the capsule from the Dragon.
Nappa: Beat Nappa with Vegeta
Raditz: Beat Raditz with Goku.
Recoome: Beat Recoome with Goku.
Saiyaman: Beat Cell with Gohan - adult only.
Supreme Kai: Beat Supreme Kai with Goku.
Teen Gohan: Beat the last Cell on Supreme Kai's planet with Adult Gohan.
Tiencha: Get both breakthroughs of Tien and Yamcha
Vegeta: Beat Vegeta with Goku on Namek.
Vegeto: Wish for it on the Dragonballs
Videl: Beat Super Buu as Hercule Stage 8
Yamcha: Beat Nappa with Tien