Boo Lore

The royal Boo family with it's current King Boo, William, is the most powerful group of all Boos.
However that power came with a price, a curse in fact.

The only reason there even is a royal Boo Family is the fate that befell William and his sister Evelyn a few hundred years ago in which the pair, specialized in the jewelry trade, came into possession of two ancient crowns with gems each.
What they didn't know was that one of the crowns had an old evil spirit sealed away inside it's gem. So when the day came of a terrible ambush of a rivaling business ending in a bloodbath, William's spirit wasn't able to rest and instead clinged to said crown which in turn reanimated him as a ghost being able to kill his opponent.
What he didn't know was that his rival too was too restless to die and got accepted by the other spirit into the gem as well.
What followed were years of torment by the two spirits being able to take over his mind and body with as little as a snap of their fingers if they so wanted.

Another side effect of the gems and in turn the spirits was the characteristics of the ancient evil.
Violent and or destructive outbursts, a seemingly endless pool of power, the ability to withstand blows others would have easily crooked from but worst of all bloodlust, turning the king and by proxy his family into vampiric beings having to feed regulary in order not to starve.
Any attempt at repressing these urges only make the later damage worse and so resistance is pointless or certain death.
Because of this very curse the royal Boo family is rather small in numbers in an attempt to keep the threat contained.

While Boos in general are a rather harmless species it it advised to generally keep away from the mansion if unannounced.