Play as Hercule:
Once you reach level 50 with Gohan, Vegeta, Piccolo and Trunks, go to the characters' specific gate marked with "50" to collect the trophies. You will find the gates here:

Gohan: Outside Gingertown
Vegeta: Northern Mountains
Piccolo: New Namek (you must find all seven Nameks to visit)
Trunks: West City

Be a True Saiyan:
Once you get the "Scouter," press Select while fighting a boss to see that boss' data.

New Ending:
Get to level 50 with Hercule (Mr. Satan) and break down the Level 50 door to KKTV in West City.

Thanks to Revolution readers Jack Bermes and Daniel Clarke!