Things You'll Need
Instructions
Press "Start" to get into your menu the instant the fight begins. Go into your Items menu and put the Syringe into your active items. Equip a weapon that is familiar to you. The Rail Gun seems to work particularly well against Vamp. Only a few fully charged shots will deplete his whole life bar.
Position the Syringe and your weapon in the equipped items box. Both of these items are necessary for defeating Vamp.
Deplete Vamp's life bar. Hold the "L1" button and continue peppering Vamp with shots until his life bar is completely gone. When his life bar is empty, Otacon will declare victory over your headset. Vamp will fall to the ground, only to get up in a daze almost immediately.
Grab Vamp immediately by holding the "R1" button when he initially gets up. Put away any weapons you have ready by tapping the "R2" button. When you have him, press the Triangle button to inject Vamp with the Syringe.
Watch the cut scene. Raiden will come to your aid against Vamp. A wave of Geckos will attack. Use your Rail Gun to eliminate the Geckos while Raiden finishes Vamp. This will take roughly 4 minutes.