Infernax

I’m not sure if this is the only way to get this achievement but here’s what unlocked it for me. Use the Konami code to start the game and select 2 players (can even use the far right option to play with only 1 controller and switch between characters with RB). Once in the game, get to a save point and select Upgrade Joe Carbine and buy one of the health potion upgrades to unlock the achievement.