Old Cartoon Network show name?

There used to be an animated show on Cartoon Network that involved these teenagers that would go and solve mysteries. Now, it's not Scooby Doo, this show had a blonde man, a young girl, and a little alien. They worked for this secret organization and the boy had a watch that contained items or something. I remember the title had something to do with ghosts and that the opening had some green slime in it. Please help me find the title, I want to show this old series to a few young friends of mine.