How's about a little background stories for these guys....
Vampire: Since the beginning of time multiple species of aliens have lived amongst us. Most of them find ways to blend in and live unnoticed by the human world, but there are those who have not had as much luck. In order to explain these interaction with aliens humans spun webs of legends and mystical creatures around them. Vampires are the human name for a species of carnivorous aliens who generally stay away from humans, but have been known to occasionally seek out our blood to sate their thirst.
Frankenstein: Before any medical procedure is approved for human testing it is first tried on animals, right? Well, Dr. Frankenstein was no exception. Before putting together his monstrous human abomination he first did a bit of animal experimentations... and this is what he made.
Mummy: The Big-Bag theory was actually a cover up of a great nuclear war between the human race. Tension between the super-powers of the time had led to a disaster that wiped out nearly the entire population of our planet. Most of those who survived were sickened by radiation and left with no suitable medical facilities for treatment. A theoretical solution to stopping the spread of radiation was to wrap the infected up in ointment soaked fabric until the radiation eventually seeped out. Unfortunately, that solution transformed the victims into mutated creatures that stay dormant for years, but reek terrible havoc when they are awake...
