To the right (the audience's left) of the Wolfman's mask in the garage (from A Gaggle of Galloping Ghosts, different from the one on the front lawn from Who's Afraid of the Big Bad Werewolf), above the Space Kook helmet... Is it just me, or is that the monster from The Scooby-Doo Project?
Even though TSDP isn't in canon, this skit during a football game establishes that Mystery Inc. not only survived The Scooby-Doo Project, but also presented the footage to the general public, only to be dismissed as trying to rip-off The Blair Witch Project (which... duh). So theoretically, they could've gone on this mystery, and kept the farmer's mask in their treasure trove of souvenirs.
Here's the mask from the original case, and here's the mask from the trailer. Keep in mind that since it is in the background, it's not given nearly enough detail, much like the Werewolf mask right next to it, so it's not identical. In fact, it could easily be the Zombie from "Which Witch is Which?" but the angular chin and the gaping mouth makes me think of the TSDP monster much more.
I took two screenshots of the trailer, one of the lawn and one of the garage, and aside from the Crystal Ball, everything else is in view. Since you can clearly tell they're screenshots (timestamps, video title, etc.) I won't upload them to the Wikia, but if anyone is interested in analyzing them, I can upload them externally and link them here. Probably not too helpful because you guys can do the same thing I did, but I thought I'd offer anyways.
Adam strickland wrote: Those were from the cartoons.
I understand, but this thread is specifically about the items seen at Mystery Inc.'s garage sale in the trailer for the Curse of the 13th Ghost. So if we didn't see it in the trailer, which only had about 15-20 seconds dedicated to the garage sale, we don't know the status of it until we see the movie, though I doubt we'll see much more there, since it's not the focus of the movie.