Here is the full list of all 12 HellGunner (EU) trophies - there are 11 gold and 1 platinum.
Get all other trophies.
Complete level 1-1.
Complete level 2-1.
Complete level 2-4
Complete level 3-1.
Complete level 4-1.
Complete level 5-1.
Finish the game.
Find the hidden box on level 1-4.
Find the hidden box on level 3-1.
Find the hidden box on level 4-2.
Find the hidden box on level 5-2.