Quantum Theory

Scene 0-2: The Womb. Once your teams split off and it's just you and one teammate on the bottom floor you'll come to a spot where the path splits and your teammate says something like "You've got good instincts, choose a path". At this point choose the path to the right and at the end will be an ammo box and an Ifrit. You'll know you're in the right area because your teammate will say "It's a dead end, but at least there's ammo". Continue fighting on until you get to the area with a bunch of spider holes surrounding a circle. Your teammate will instruct you to find a way out or you'll run out of ammo, ignore this and let a group of the spiders gather close together and then BAM! Achievement unlocked. Needless to say, do this on easy so that you can allow them to encircle you.