When the battle starts, use the syringe. Shoot at her dolls, the blue on first. Eventually, she will control Meryll. Inject Meryll with the syringe, and continue to attack the blue doll. She will again try to control Meryll, so inject her again. Now you can knock away her blue doll. Pick it up when she drops it. She can no longer control the dead bodies. Now shoot the orange doll. Once you get it, equip it, hit Mantis with it, then shake the controller. You should win. (Note: this counts as a stamina kill)
Chat with our AI personalities
Once you beat the beauties in their big 'suits' and you have to re-kill them in normal form use a gun that uses tranquilizer rounds to knock them out
you dont
In Act 5 of Metal Gear Solid 4: Guns of the Patriots on the PlayStation 3, you must inject yourself with the syringe in able to engage in combat with Screaming Mantis. To do so, press Start to open the pause menu. In the Item menu, go to the Recovery Items tab and select the Syringe and put it in your inventory. Then exit the pause menu to return to the game. Hold down L2 to open the Item window, select the syringe and follow the instructions onscreen to inject yourself. You are now able to use your weapons against Screaming Mantis. At some points during the boss battle, she may shoot fireballs at you. If you are hit you must inject yourself with the syringe again.
it makes you have unlimited ammo
its available when you get the mkII