The What If Saga Stages are needed for 100% completion in story mode, and are unlocked after winning an "impossible battle". Unlock the following What if Saga Stages by performing the corresponding tasks:
STAGE - HOW TO UNLOCK What-if Beautiful Treachery - Defeat Dodoria with Gohan and Krillin in mission 01 of the Frieza Saga "A Pursuer Who Calls Death". What-if Destined Rivals - Defeat Gohan with Goten in mission 01 of the Majin Buu Saga "Training With Goten". What-if Fateful Brothers - Defeat Raditz with Piccolo in mission 00 of the Saiyan Saga "Mysterious Alien Warrior".