Successfully complete the game.
Similar to Prestige for Call of Duty, Legacy Mode can be unlocked after you level up to Level 75 on multiplayer online. The game will ask you if you're interested in Legacy Mode, where you were start from the beginning at Level 1, losing all your boosters, unlocked guns, and unlocked mods. You will receive a new emblem with a diamond at the corner and new negative boosters which will hinder you but increase your cash intake. You will be allowed to keep treasures, unlocked special guns from treasure sets, and unlocked skins.
Piggyback Strategy Guide Logo Emblems
Press Up, Right, Down, Left, Up, Left, Down, Right on emblem editing screen to unlock some Piggyback logo emblems.
Beat all five Co-op Adventure maps on Crushing and you receive a silver star by your rank. To unlock the Crushing difficulties you must beat the maps on any difficulty beforehand.