Sebastian is the 3rd vampire that you have to kill. You will meet him when you are about to get the 'nexus stone'. This boss is one of the hard ones and will take a couple of deaths and f-words before you beat him. But if you want to beat him the easy way....Just stand there. If you just stand there he will not attack you and the steam around the room will kill him (you may have to die once). Whenever he is about dead the steam may not hit him anymore. During this time u can attack him becuase he will be kinda 'frozen'. He once again will not be able to attack you and the Nexus stone will soon be yours. Remember dont move!