Secret Mira boss Wight:
Defeat all Villainous Parties in the game, which are marked by a red crown icon on the map. Once all Villainous Parties are defeated, Mira can be found on the "Land Of The Kais" planet. He is a Level 100 enemy that has lots of health. Defeat him to get the "Down With The Demon Realm!" trophy.
Find a cave with lots of rare crystals. Destroy the rare crystals, create a manual save, then reload the save for everything to respawn. Destroy the crystals again, and repeat the process as many times as desired. Sell the items from your inventory to merchants for easy money.
Easy Rare Z-Orbs:
Rare Z-Orbs can be found in a variety of ways, but two of the easiest are found on every map in the game. While flying around, look for Phantom Airways and Timed Z-Orbs. Activate a Timed Z-Orb to make additional Z-Orbs appear —- some of them will be rare. Look for the Phantom Airways, which are golden circles in the sky. Flying into a Phantom Airway sends you through an air-tunnel filled with Z-Orbs, including some Rare Z-Orbs. They reset locations every time you re-enter a map region. Simply fly into a Phantom Airway and collect the Z-Orbs, then go to the map screen, and re-enter the same area for a new Phantom Airway to appear. Repeat this process as many times as desired.
Successfully complete one of the following tasks to get a trophy:
Dragon Ball Master (Platinum): Obtain all trophies.
Fountain of Knowledge (Gold): Unlock 400 entries in the Z Encyclopedia.
A Super Warrior Is Born (Silver): Acquire 100 Super Attacks or Masteries in the Super Attack Skill Tree.
Heavy Medal (Silver): Collect 100 D Medals.
Shenron's Favorite (Silver): Summon Shenron 10 times from the Dragon Ball menu to make a wish.
Thirsty for Knowledge (Silver): Unlock 200 entries in the Z Encyclopedia.
Turtle School Legend (Silver): Complete 50 Turtle School training challenges and report to Master Roshi.
Can't Touch This (Bronze): Get 50 instant victories on enemies.
Do-Gooder (Bronze): Complete 10 sub stories.
Get out of My Head and Turn into My Car (Bronze): Build a hovercar.
Getting Greedy (Bronze): Summon Shenron 5 times from the Dragon Ball menu to make a wish.
Helping Hand (Bronze): Complete a sub story.
Highly Skilled (Bronze): Acquire 50 Super Attacks or Masteries in the Super Attack Skill Tree.
Let the Building Begin! (Bronze): Build a machine part.
Medal Madness (Bronze): Collect 10 D Medals.
Newfound Power (Bronze): Acquire a Super Attack or Mastery in the Super Attack Skill Tree.
Not Worth My Time (Bronze): Get an instant victory on an enemy.
Only the Finest (Bronze): Make 5 full-course meals.
Push It to the Limit (Bronze): Complete 10 challenges at a Training Grounds location with any character.
Robot Rider (Bronze): Build a Bipedal Robo Walker.
Tell Me More (Bronze): Unlock an entry in the Z Encyclopedia.
The Power of Friendship (Bronze): Use 10 Super Attack Assists.
The Voice in My Head (Bronze): Receive a telepathic message from King Kai.
There's Nothing Like a Home-Cooked Meal! (Bronze): Make a full-course meal.
Turtle School Master (Bronze): Complete 20 Turtle School training challenges and report to Master Roshi.
Turtle School Trainee (Bronze): Complete a Turtle School training challenge and report to Master Roshi.
Who Needs a Phone? (Bronze): Receive 20 telepathic messages from King Kai.
Wish Maker (Bronze): Summon Shenron from the Dragon Ball menu to make a wish.
Z Combo Zealot (Bronze): Perform 10 Z Combos.
Additionally, there are 13 secret trophies:
Bye-Bye, Buu (Gold): Complete the Majin Buu Saga.
Down with the Demon Realm! (Gold): Win the battle against Mira.
Tough Enough (Gold): Complete a Level 10 challenge in the Training Room.
Earth's New Champion (Silver): Complete the Cell Saga.
Emperor No More (Silver): Complete the Frieza Saga.
Evil All Around (Bronze): Defeat 20 Villainous parties.
Purging the Plague (Silver): Defeat 30 Villainous parties.
Worse For Wear (Silver): Complete the Saiyan Saga.
A Dark Omen (Bronze): Defeat your first Villainous party.
Demolition Artist (Bronze): Destroy 10 boulders blocking caves.
Excavator (Bronze): Destroy a boulder blocking a cave.
Flashy Finish (Bronze): Win a battle with a Super Finish.
Former Foe (Bronze): Win the simulation battle against Piccolo.