With real ghosts, possibly
Ubisoft's free-to-play online shooter, Ghost Recon Online, just got a Halloween update. Nothing screams horror and pranks like tactical multiplayer combat. The surely terrifying Halloween content pack comes with new player skins, different weapon stats, and six new weapons. If you can't shoot a missile out of a witch's broom, I'll be extremely disappointed.
On top of the themed shenanigans, a clan system has also been implemented. These social groups can be customised through the use of clan tags and clan crests. Apparently this is just the first phase of the system, with more being added early next year; specifically competitive elements.
For new players, the Beginners Playlist has been introduced -- teaching newbies the basics and pitting them against other players with an appropriate level of experience. This, and all the content from the 0.9.0 patch is available now.