Level 1.On Planet Namek ofter Frieza killed Krillin
Level 2.While training in the after life
Level 3.While training in the after life
Level 4.After seeing Pan cry Goku got enraged and went SSJ4
Gohan
Level 1.While training in the room of spirit and time during the Cell Saga
Level 2.After Cell killed Android #16
Level 3.Never went
Level 4.Never went
Vegeta
Level 1.Training before the Androids appeared
Level 2.When turing into Majin Vegeta during the Boo Saga
Level 3.Never went
Level 4.Bulma builds him a brute ray which makes him go SSJ4
Goten
Level 1.While training with Chi-Chi
Level 2.Never went
Level 3.Never went
Level 4.Never went
Future Trunks
Level 1.After Gohan was killed by the Androids
Level 2.Never went
Level 3.Never went
Level 4.Never went
Chibi Trunks
Level 1.While traing with Vegeta in the beginning of the Boo Saga
Level 2.Never went
Level 3.Never went
Level 4.Never went
Brief Note: When Goku and Vegeta go SSJ4 it happens in DBGT but everything else takes place in DBZ
