Use melee attacks and do not let him regenerate himself. If you cannot avoid him regenerating, keep using your ultimate attack until he is dead. You will have to defeat him four times because of The Senzu Beans.
To transform during gameplay, highlight a character that can transform and press Right. Choose your transformation state. Then, fill your Kai meter to just over half. Press Down + Circle to transform. Note: If you get hit with no Kai remaining, you can transform back into your normal state.
Unlock the following characters by performing the corresponding tasks:
CHARACTER - HOW TO UNLOCK Adult Gohan (Mystic form) - Defeat Vegeta in Chapter 4-A-B 5. Adult Gohan (Super Saiyan form) - Defeat Frieza in Chapter 1-8. Adult Gohan (Super Saiyan 2 form) - Defeat Broly in Chapter 2-6. Bardock - Defeat Bardock as Goku in Chapter 5. Broly (Legendary Super Saiyan form) - Defeat Frieza in Chapter 4-A-B 6. Cell (Super Perfect form) - Defeat Cell in Chapter 2-5. Cooler (Final form) - Defeat Pikkon in Chapter 4-B-A 5. Dubora - Defeat Dubora in Chapter 2-2. Frieza (100% Full Power form) - Defeat Frieza in Chapter 3-2. Future Trunks (Super Saiyan form) - Defeat Gotenks in Chapter 4-2. Gogeta - Complete the straight path in Chapter 6. Gohan (future form) - Complete Chapter 5. Goku (Kaioken form) - Defeat Krillin in Chapter 1-2. Goku (Super Saiyan form) - Defeat Janemba in Chapter 1-9. Goku (Super Saiyan 2 form) - Defeat Fake Goku in Chapter 2-2. Goku (Super Saiyan 3 form) - Defeat Majin Vegeta in Chapter 3 Goku (Super Saiyan 4 form) - Successfully complete Story mode. Alternately, defeat Kid Buu in Chapter 7 with all cities over 60% health. Gotenks (Super Saiyan form) - Defeat Gotenks in Chapter 1-5. Gotenks (Super Saiyan 3 form) - Defeat Cell in Chapter 3-A-4. Gotenks - Defeat Gotenks in Chapter 1-4. Janemba - Finish the Story Mode. Krillin (Unlock Potential form) - Defeat Goku in Chapter 5-1. Majin Vegeta - Get a final rank of "A" to "Z" in the last chapter. Majon Vegeta and SSj4 Goku - Complete the last chapter with 60% or more health for all cities. Piccolo (Fuse with Kami form) - Defeat Cell in Chapter 2-1. Pikkon - Defeat Janemba in Chapter 2- 9. Super Buu (with Gohan absorbed form) - Complete Chapter 7-3. Super Buu (with Gotenks absorbed form) - Complete Chapter 7-2. Teen Gohan (Super Saiyan form) - Defeat Cell in Chapter 3-8. Teen Gohan (Super Saiyan 2 form) - Defeat Teen Gohan in Chapter 3-9. Vegeta (Majin form) - Defeat Vegeta in Chapter 4-7. Vegeta (Super Saiyan form) - Defeat #18 in Chapter 2-3. Vegeta (Super Saiyan 2 form) - Defeat Janemba in Chapter 2-7. Vegeto and Gogeta - Complete the last chapter choosing either path. Vegetto (on all modes) - Defeat Super Buu on Chapter 6 bottom path. Vegetto (Super Saiyan form) - Defeat Kid Buu in Chapter 5-B-9. Vegito - Complete all seven chapters.
The following trick only works in Training mode. ChooseGoku as your character and anyone as the opponent. Set the opponent to "Do Nothing" and set their Ki Blast Defense option to "Deflect-Back". Then, shoot a Ki Blast at them, wait a moment, then press Up + Circle to do your Spirit Bomb, but don't charge it up. If timed correctly, the attack will fly over the Ki Blast that your opponent has deflected back to you, and they will begin to take damage from your attack while the Ki Blast comes toward you. Once the deflected Ki Blast hits you, immediately press Select to refill your energy. Before your super move is completely finished hitting your opponent, prepare another that's fully charged. Your opponent will suddenly stop taking damage and your first attack will disappear. Once your fully charged attack starts flying toward your opponent, watch the attack. As soon as your opponent starts getting hit by your attack, you should see a second Spirit Bomb separate from the first and fly past your opponent before exploding. You can also do this with anyone else who has an "Energy Ball" super move, except for Kid Buu. It doesn't work with him because he is so short that whenever you do the first one, it always flies too low and cuts through the Ki Blast. Also, be sure to throw a Ki Blast at the beginning; if it doesn't hit you, you will enter a "recovery time" after launching the attack where you will not be able to move.