The mansion is the home of Sylvester, a real vampire, who lives alone.
The Richie Rich/Scooby-Doo Show
Sylvester said he had a cook who was off the night that Scooby-Doo, Scrappy-Doo, and Shaggy Rogers came there for help after getting a flat tire, but that was a lie. When he can't get blood he drinks canned tomato juice. (A Fit Night Out for Bats)