Here are some eggs I found when I had beaten the game with only 95% and I was bored.
Egg#1:How to win Kid Goku
Go to th Magin Buu Saga at mission 01 where you are Goten facing Gohan. You are supposed to die, but win and you will win a new saga. Play it until you are on the map with Goku. Go to Kami's Lookout. Talk to King Kai, who will give you a battle against Grampa Gohan. Win and You will Get Kid Goku and a thing to fuse with someone to get Grampa Gohan.
Egg#2: King Kai's rap
Go to the Evolution Z. Wait for about 45 seconds. King Kai will suddenly start to rap(very, very badly)
Egg#3:Fake characters
Go to the Dragon Library after winning Great Ape Raditz and Great Ape Nappa. Go to their profiles and scroll to the bottom. You will see the following sentence: "Nappa/Raditz does not transform in the show. He was made especially for the game."
Egg#4:Special Greetings
As in all DBZ games, if 2 characters have any relation, they say something to each other. Here are 3 that I remember.
Baby Vegeta vs Trunks. Trunks:"Father, is that you?" Baby Vegeta: "Today is your new birthday...as my slave!"
Goku vs Vegeta. Goku: "Even a reject can surpass an elite if he trains hard enough. Vegeta: "Let me assure you, this is one battle that no amount of training can prepare you for!"
Android 18 vs Super 17. 18: "This... this is for Krillin!" Super 17: " ou'll be with him again soon"
Egg#5:Ultra Spirit bomb
When you are Goku, stall the opponent until the number next to your life bar is at 7 (this might take a while). Go into Kaoken (not kaoken attack). Charge to full and do Spirit Bomb. It will be impossible to dodge and it will kill them as long as they have under 5 life bars.