Below is the solution I wrote for the "Vampire Slayer" achievement on TA.
My solution is to stamina kill Vamp on the harder difficulties (Hard, Extreme, etc).
STEP 1: Once the battle starts, switch to your M9 and traq him. He will scream and go under.
STEP 2: Once he is swimming in the pool, switch to your grenade launcher or the stinger missile and shoot at the water itself (anywhere, it doesn't matter). This will do very little stamina damage, but it adds up over time.
STEP 3: Wait for Vamp to jump out of the pool. When he does, turn to the bottom of the screen: there is a railing you can grip from. Do it. Vamp will jump around throwing knives, but don't worry - none can hit you while you are gripping the ledge.
STEP 4: After a few seconds Vamp will begin to slowly walk towards your location. He will have the red aura around him (which means he is invincible). He will position himself in front of you, drop his red aura and get ready to slash you. THIS IS IMPORTANT: Your timing is critical here. As Vamp begins his cut-you-up animation, press the triangle button. If you do it correctly you will hear Vamp slice through the air, and you may even hear him hit Raiden, however you will not lose health or get damaged while Raiden swings himself back over the railing. Then you just need to pummel him with your One-Two combo and send him back into the pool.
STEP 5: Repeat Steps 2 - 4.
If you have the infinite wep wig, or the infinite grip wig, they are useful here, but not necessary.
Questions, corrections and neg vote justifications below.