Win the level 3 weapon challenge bets at the PMC Villa with your allies to unlock a random alternate costume. Talk to Fiona at your PMC to access the challenges (Gun Emplacements, Pistol, Grenade Launcher, and Sniper). Each character has a total of five costumes. Note: Bet the maximum money for the level 1 and 2 challenges then save and reload the game until you win. Bet the minimum money for the level 3 challenge.