Vampire Hunters

A ghost comes to you after reaching the final point of a stage where you have an objective,around the 20min mark,i got it in the first stage,i just closed all portal inside the building then left only 1 outside open,then just survive,when the ghost comes(he would be huge so you won't miss it) just run up the platform then jump down,rince and repeat till you get the achievement,then when you get it you can close the remaining portal/portals