Bardock
At the start of Dragon Universe mode, just fly over to Raditz's spaceship. You should see a "???". Go into it, and you should get him.

Or you can keep checking the Sayian Space Pod, and at one point you will be able to go to it and locate Bardock. This was located near the end of story mode when playing the first time.

Brolly
As Goku, finish Dragon Universe mode three times or more. On the third time, you will fight Brolly. Beat him to have him.

Make your way to the Desert/Mountains and speak to Kibito southwest of the next marker. After you fight Buu inside himself, Goku and Vegeta will sense a different energy. Then, go to the next marker to face Broly. Beat him to have him.

Captain Ginyu
Beat Captain Ginyu as Goku in Dragon Universe mode.

Android 16
You can locate Android 16 at Plain amid the south island. Bring him to Bulma in West City (Krillin's Dragon Universe mode the second time).

Android 17
Beat Android 17 as Piccolo in Dragon Universe mode.

Android 18
Finish Dragon Universe mode as Krillin.

Cell
Beat Cell as Teen Gohan in Dragon Universe mode.

Cell Jr.
Beat Piccolo in Dragon Arena when he broken in. Note: You need to be at level 20 to 40.

Gogeta (Vegeta)
Purchased from Skill Shops is random, when you have the Black Membership Card.

Or you can play as Vegeta in the second Dragon Universe. In the Buu Saga, you should locate Bulma in a plain somewhere. Talk to her, and she will tell you to visit her later. Then, fly to West City. Pick up the present she has for you. Next, fly to the red dot to the south. Once there you will meet Super Sayain 4 Goku. Beat him and you will receive the capsule for Gogeta.

Gohan
Finish Dragon Universe mode as Teen Gohan.

Goten
Beat Goten as Gohan in Dragon Universe mode.

Gotenks
Purchased in the Capsule Shop.

Cooler
Beat Frieza. SS Vegeta will appear under the location where he was conquered. After beating SS Vegeta, go to Cooler's red dot. Beat Cooler to have him available.

Dabura
Beat Dabura as Gohan in Dragon Universe mode.

Dr. Gero
Beat Dr. Gero as Yamcha in Dragon Universe mode.

Frieza
Beat Frieza as Goku in Dragon Universe mode.

Great Saiyaman
Finish Dragon Universe mode as Gohan.

Hercule/Mr. Satan
Help him out in Piccolo's Dragon Universe mode (Majin Saga) at the desert, and talk to Videl at Central City.

Kid Buu
Beat Kid Buu as Goku in Dragon Universe mode.

Recoome
Beat Recoome as Goku in Dragon Universe mode.

Saibaman
Beat Nappa in Dragon Arena when he broken is in. Note: Your level has to be between 10 to 20.

SSJ2 Gogeta
After beating Broly in Dragon Universe mode, beat Gotenks at the World Tournament Arena.

Super Buu
Beat Super Buu as Goku in Dragon Universe mode.

Supreme Kai/Kaioshin
You can locate him at the plain before you go to the final battle in Gohan's Dragon Universe mode.

Kid Goku
As Goku in Dragon Universe mode, at the beginning search for someplace that reads "Grandpa Gohan's house". After you go to it and Goku talks to his grandpa, you will have Kid Goku available.

Or you can simply finish Dragon Universe mode as Brolly.

Kid Trunks
Beat Majin Buu as Vegeta in Dragon Universe mode.

Majin Buu
Beat Majin Buu as Goku in Dragon Universe mode.

Omega Shenron
Once your invited to fight against Gotenks at the tournament in Dragon Universe mode, visit Bulma in West City. Beat Gotenks to have Omega Shenron available.

Uub
When you are fighting Kid Buu, use the Spirit Ball technique and win.

Vegeta
Beat Vegeta as Goku in Dragon Universe mode.

Vegito (Goku)
Beat Super Buu as Goku in Buu's Body in Dragon Universe mode.

Vegito (Vegeta)
Beat Super Buu as Vegeta in Buu's Body in Dragon Universe mode.

Videl
Make your way to the Plains as Gohan in Dragon Universe mode.

Teen Gohan
Finish Dragon Universe mode as Kid Gohan.

Trunks
Finish Dragon Universe as Vegeta.

Trunks (young)
Beat Majin Buu in Dragon Universe mode as Vegeta.

Dragon Radar
Keep searching all around the map as soon as you start. Now pick a point and go in a small angle so that you move out just a little bit at a time. You will see a marker appear with "?????". This can take time, and you may come across some money or capsules, but you will find the Dragon Radar along with two Dragon Balls in the first area. Do the same type of search on each area to find everything; even places to battle and level up, along with friends who will give you skills and even a level up or two.

Gogeta capsule
Simpl play Dragon Universe mode as Goku or Vegeta. Go on until you get an invitation from Goten and Trunks to fight in a fusion battle instead instead of fighting Buu or Brolly. Win the fusion battle to receive the Gogeta capsule.

SSJ4 Gogeta Fusion
On the Majin Buu map, beat Omega Shenron as Goku.

SSJ4 Gogeta Fusion
On the Majin Buu map as Vegeta, enter all the red dots and the other areas beside the red dots after every red dot event.

SS4 Goku
Have 30,000 Zeni and make your way to the Skill Shop It will rarely appear. If you win the Adept or Advanced Tournament first, it may appear quicker.

After beating Kid Buu with the Super Spirit Bomb, and before you go to fight in the World Tournament, go to one of the islands just north of where the compass is on the map. You will see a "???". Land there and you will receive SSJ4 for Goku. Note: You may have to finish Dragon Universe mode a few times before you do.

After beating Brolly, do not go to Vegeta or Bulm. Instead, first go to where the World Tournament area is at in Dragon Universe mode. Then search around those islands and you should locate a "???". Goku will start saying things like his head is throbbing. He will turn Super Sayian, then back to regular Goku. You can then return to Bulma or Vegeta.

SS4 Vegeta
Purchase it at the Skill Shop for 30,000 Zeni, after you receive the Black Membership Card.

Super Sayain 4 Goku skill
Note: You may need to finish Dragon Universe mode first. After your first fight with Buu to your final fight with Kid Buu, search the map after each fight. At some point you will locate Goku's Super Sayian 4 skill. This has happened just before fusing with Vegeta to fight Super Buu, and it appeared as a "?????" at the bottom right area. However, this could vary from game to game.

SSJ4 Vegeta Transformation capsule
On the Majin Buu map, make your way to West City as Vegeta to see Bulma.

Dragon Balls
Find the Dragon Balls in Dragon Universe mode that are listed below, and you can wish for a Breakthrough Capsule, Memories, or some rare Green Capsules.

Two Dragon Balls are in Saiyan Saga (Earth)
The first ball is by the white plains; around Red Ribbon Army Base.
The second ball is between the upper two main islands.

Two Dragon Balls are in Frieza Saga (Namek)
The third ball is at the upper right island.
The fourth ball is on the left island near map border, southwest of the upper left island.

One Dragon Ball is in Cell Games (Earth)
The fifth ball is found where the compass is on the map in the water.

One Dragon Ball are in Buu Saga (Earth)
The sixth ball is by the main island towards the middle by North City.
The seventh ball is at a little sandbar island (resembles a beach) near the martial arts tournament.

Baba Crystal Balls Movie 00
Access every Ultimate Move skills and the Baba Crystal Balls Movie 00 can now be purchased at the Skill Shop.

Baba Crystal Balls Movie 01
Purchase the Baba Crystal Balls Movie 00 and the Baba Crystal Balls Movie 01 can now be purchased at the Skill Shop.

Breakthrough (All Character)
Can be purchased for 75,000 for each character at the Skill Shop after you have Baba Crystal Balls Movie 01 and obtain all Breakthroughs for each playable character in Dragon Universe mode.

Ultimate Skill Moves (All Character)
Can be purchased for 50,000 for each character at the Skill Ship after you have all characters available.

Dragon Arena
Finish Dragon Universe mode with every unlockable characters in that mode, this includes Broly, teen Gohan, and high school Gohan.

Grandpa Gohan's House
Just play as Kid Gohan in Dragon Universe mode, the second time through. Instead of fighting Piccolo in the Mountains, go to Grandpa Gohan's House and beat Goku.

Cell Games Tournament
Beat Cell when he appears in the Dragon Arena matches.

Bonus items
Have a saved game from Dragon Ball Z Budokai 2 on your memory card to receive a Silver Membership Card, Babidi's Pot, and Bardock.

Membership cards
These are in Goku's Dragon Universe. All three membership cards can be located on an island just north of the "Golden-Gate" looking bridge. After going through Goku's Dragon Universe a couple of times, all three will be there to be obtained.

To receive all membership cards, look all over the map and acquire all the "???" items. At some point you will find a Black Membership Card. Go in there once again and you will receive all the membership cards.

Hints & Tips

Dragon Rush
Use this trick to win in Dragon Rush roughly 80% of the time in every match. If you start Dragon Rush, first: X; second: Triangle; third: Square. If your foe starts Dragon Rush, use Square, Circle, or X.

Special versus matches
Before each match (except Dragon Universe and Arena). almost every character has a special scene. Here they are:

Goku vs. Vegeta
Goku vs. Frieza
Goku vs. Bardock
Goku vs. Brolly
Kid Goku vs. Tien
Trunks (Adult) vs. Vegeta
Kid Goku vs. Piccolo
Kid Gohan vs. Piccolo
Teen Gohan vs. Cell
Krillin vs. 18
Piccolo vs. 17
Uub vs. Kid Buu
Ginyu vs. Recoome
Vegeta vs. 18
Trunks vs. Cell
Majin Buu vs. Kid Buu
Kid Goku vs. Yamcha