So on my third try, I finally got it. How does one beat Vamp in Metal Gear Solid 4: Guns of the Patriots. Easy. Use the syringe! First kill him: use long range/explosive weapons. (2)Then equip the syringe as your item. Then, when he’s getting up and doing his whole “I’m invincible and a jerk” thing, (3)press R1 to headlock him. (4)The “Syringe – Press Triangle” will come up. Press triangle. Done.
The next part is to take out the GEKKOs with the Rail Gun/.50 cal. Shoot the ones with red lights when you see them. They’ll Self Destruct if you don’t and you’ll lose. Kill the others if they get to close. Once the last one is destroyed, it’ll cutscene. Done.