I was flipping through the Monster Manual when it suddenly came to me, I should make an invincible vampire to challenge my players. Normally I just come up with some clever gimmick for the NPCs to take advantage of to make an adventure more challenging, but my players are in need of something a little more powerful (and if at all possible, terrifying). My players are currently on a high seas adventure, trying to return to land after having run away from a failed adventure.

What I plan on doing on doing for the vampire is, so far...
-Giving him some wonderous item that has Repel Wood on it, making him practically immune to normal stakes
-Equiping him with sundark goggles, which would allow him a full round action when suddenly caught in sunlight but also making him immune to any spell effects that rely on a burst of bright light
-Turn Resistance Feat of course
-Base Race: Aquatic Troll, making him immune to both the vamperic weakness of running water (1/3 of HP total per round underwater? I don't think so!) and also granting him massive regenative properties. Even beheading him would not slow him down... once he grew a new head that is.

So any other ideas you think I could use to make him more deadly? My chosen EL is between 11-15.