Character Trophy Locations & Guide
There are a total of 5 Character Trophies for you to collect in the game. Four of them come from leveling a character to level 50 and finding that character's Level 50 Character Gate, smashing it down and collecting the trophy on the other side. The only trophy that you don't find this way is Goku's. You'll get Goku's trophy after beating Cell with Gohan.
The hardest part of unlocking these gates won't be finding them, it'll be level your characters up to level 50 in order to open them. Out of all the locations in the game, the best one that I know of is in the Snowy Mountains. Past the humanoid enemies in the back you'll find a lot of higher level animals. I spent a few hours grinding a screen with 6 or so wolves to get level 50.
Vegeta's Level 50 Character Gate
Location: Northern Mountains
In the northwestern portion of Northern Mountains you'll find Vegeta's Character Gate. It's inbetween Dr. Gero's Lab and Vinnie's House - two places you should be familiar with from earlier in the game. Inside the gate are two Golden Destroyer enemies that are pretty tough.
Piccolo's Level 50 Character Gate
Location: New Namek
This door is located in the room behind where you fight Cooler on New Namek. In order for you to travel to New Namek you'll need to collect all 7 of the Missing Namekians and then take the space ship found outside Capsule Corporation.
Trunks' Level 50 Character Gate
Location: Triceratops Jungle (South of West City)
Fly over to West City and travel out of the southern end of it, you'll find yourself in the Triceratops Jungle. Trunks' Character Gate is due east from this location. It's pretty hard to miss. Once you pass through the gate, you'll need to defeat the Golden Destroyer to open the door leading to this character trophy.
Gohan's Level 50 Character Gate
Location: Outside Gingertown
Just north of where you land outside of Gingertown you'll find Gohan's Level 50 Character Gate. You'll have to clear a bunch of enemies after smashing down the gate before you can get to Gohan's Character Trophy.