Metal Gear Solid 4 Guide - Act 4: Twin Suns
Underground Supply Tunnel / Boss: Vamp
With Vamp's arrival on the scene we now need to take him down, despite his immortality! This boss fight itself is actually pretty easy however. Vamp moves very quickly, but as he's jumping and sprinting all over the arena he won't actually damage you. Any major blows will come after he runs directly at you. Take this opportunity to throw everything you have at him – you should be able to knock him over most times before he gets too close. A gun like the PKM which has a massive magazine (needing few reloads) is a great choice here.
Shoot Vamp as he moves towards you
Once you get his health near the bottom, equip the syringe Naomi gave you in the equipment inventory and finish him off with your main weapon. With all his health gone, he'll fall flat on the ground and you need to run over to him, unequip your weapon and initiate CQC once he stands up. Press Triangle when prompted and you'll ram the syringe into his neck thus combating Vamp's immortality-inducing nanomachines.
(Cut Scene 12, Length 03:26)
Heaps of Gekkos now storm into the arena as Raiden tries to finish off Vamp.
The Railgun we need to use for this fight will already have been selected during the cutscene. Ready it as with any gun, then press Triangle to use the scope and charge the weapon. To take down the Gekkos effectively you need a fully charged weapon with all six power bars filled up. This allows for one hit kills (you can even kill multiple Gekkos at once if they are standing in a line), though if you get pushed back you can shorten the charge to prevent them from detonating themselves. If you see them crouch down and their red lights begin to flash it means they are about to blow up, so focus on those ones! Back yourself underneath the outcrop of rocks to the north from where the cutscene ends for a decent position for all this. With no peripheral vision, this area protects you from all but one direction. If you need more ammo either buy it from Drebin (killing all these Gekkos generates heaps of cash!) or find extra rounds by Metal Gear Rex.
The Rail Gun makes mincemeat of the Gekkos
This fight will take about four minutes, with multiple waves of enemies (don't assume it's over until the cutscene plays as it does go quiet for a while in the middle). Once Raiden has finished doing his job on the right half of the screen (in tandem with the amount of Gekkos you are killing), a cutscene plays.
(Cut Scene 13, Length 10:35)