After you beat them, you fight Screaming Mantis. She's kind of a gimmicky fight. Use the Syringe on yourself so she can't affect your nanomachines. Then take Meryl down - either use the syringe on her in CQC, throw her down in CQC, or shoot her with a tranq gun. Your targets are Mantis' dolls - the red one, Psycho Mantis, and the blue one, The Sorrow. Keep the fire up on them - the XM8 was the best weapon for this due to its accuracy and high rate of fire. Take down Mantis' puppets with CQC, tranqs, or guns so they're not shooting at you. Mantis has this really weird attack where she throws knives at you, and there doesn't seem to be any way to dodge it. You can interrupt that attack by hitting either of her dolls. She'll also close in for a melee attack - it's occasionally a two-hit combo, so keep dodging. She'll also shoot fireballs from Mantis at you; if she hits you, use the syringe again.

After hitting her dolls a couple of times, Mantis will make Meryl shoot you, and then shoot herself. Tranq her to keep her down. Once you've hit a doll enough times, she'll drop it. Pick it up - use the Solid Eye to locate it - and equip it as a weapon. The Mantis doll is lethal, the Sorrow doll is not. The Mantis doll worked fine as soon as I hit her with the fireball and the fight was about over; the Sorrow doll didn't work, for some reason. Once I had the Sorrow, I kept shooting at Mantis and she dropped that too. I ended up beating her with the Mantis doll. In the Beauty section, her doll is in one of the hallways on the lower level (the one on the north side).I couldn't tell whether or not getting the Sorrow had anything to do with it. Deal with the Beauty however you please.

Run forwards through the hallway. Eventually you'll reach some of those sentry-bots. Use heavy weapons - shotguns, machine guns, grenade launchers, and rocket launchers - to cut a path through them. Eventually you'll reach the hallway with the Microwave room. Move forward down the center of the hallway. Hammer on the triangle button aas much as you can; if you get at least near the exit, you'll pass.

Metal Gear Solid 4 Walkthrough