The Vamp boss fight in "Metal Gear Solid 4" doesn't have as many nuances as his fight in "Metal Gear Solid 2" -- he won't pin your shadow to the ground, and you don't need to deal with a pit of lethal water -- but that doesn't mean it's straightforward. While most of the battle consists of unloading your best assault rifle or submachine gun at Vamp while keeping your health up with rations, there is a trick at the end: You need to inject Vamp with the syringe given to Snake by Naomi to keep the enemy's health from regenerating infinitely.
Equip your best assault rifle or submachine gun and begin firing at Vamp as he leaps around the room. Guns with high rates of fire, such as the MP7, work well if you have them, but even the basic M4 Custom can get the job done.
Equip the Solid Eye to keep track of Vamp on the radar. The boss continually jumps about the piles of debris, making it easy to lose his position without the radar turned on.
Run to the side whenever Vamp jumps vertically in place, a sign he's about to throw knives at you. Even if you get hit, however, Vamp's knife attack does very little damage.
Roll and dodge sideways or backwards to avoid Vamp's leaping melee attack. This attack does more damage than the knife attack and can knock Snake over. If your health gets low, temporarily switch from the Solid Eye to a ration to heal. The arena has some rations scattered about the debris if you run out.
Continue shooting Vamp until his health runs out and he falls down. Once he collapses, immediately unequip your gun and grab the syringe from the item menu.
Run behind Vamp and press "R1" to grab him with CQC as soon as he stands up. Press "Triangle" to inject Vamp with the syringe and win the fight.
Tips & Warnings
- If you don't make it to Vamp in time to inject him with the syringe, his health appears to fully recover. In reality, a few additional shots will quickly knock him down again, giving you another chance at using the syringe.
- No matter which weapon you use against Vamp, the game counts it as a non-lethal kill. To stick to a fully non-lethal run, however, try the M870 shotgun using V-Ring ammo. If you don't have this gun, the regular tranquilizer pistol also works, but hitting Vamp repeatedly with a handgun takes a great deal of patience.
- The Solar Gun, earned by defeating the FROGS and all Beast bosses non-lethally on an earlier playthrough, takes down Vamp in a single shot.
- Due to Vamp's high speed and agility, handguns, explosives and sniper rifles don't work well against the boss. If you do manage to hit Vamp with a sniper rifle shot, however, it knocks him down temporarily.