Sweet Justice Trophy in Costume Quest
Complete the game.
How to unlock Sweet Justice
There are 3 areas to the game. This should be the last trophy that you get in the game unless you want to go through another playthrough. Go through the corn field maze to get to the final boss. Below I'll tell you who that boss is and how to defeat him because it's the hardest fight in the game.
Big bones is your final boss and he's, well, HUGE! He hits hard and he hits multiple party members at the same time. I beat him way under leveled but it was a pain in the butt so I suggest that you go into this fight at level 10 or higher because any lower than that and you'll get pretty frustrated. The following is the strategy I used with an under leveled party so works even better if you're at level 10.
You should have the pumpkin, ninja and Statue of Liberty in your party. If any of these 3 are absolutely essential I would say it's the pumpkin. The pumpkin's special ability does massive damage to big Bones and not having that extra damage can make or break the battle.
Big bones has the same attack strategy throughout the entire fight. He has 2 attacks in his first form. One is he swipes you with his scythe hitting the entire party and the other is a really powerful attack aimed at one member. Every 3 turns he will use his powerful attack. Before he uses this attack you should use the ninja's special ability to protect the party member with the lowest HP at the time. After his powerful attack that's when you use the Statue of Liberty's anthem ability to heal the entire party. Rinse and repeat this process until you reach his second form.
Once he gets down to 1000 HP he'll eat more candy and he'll have one attack. His attack is an attack that targets one member and it's just as powerful as his most powerful attack from last form. Some party members could die while fighting him in this form but keep doing the same strategy as before and you should outlast him.
Once you defeat him you'll unlock your trophy.