The Pit (1981)
This message board alone illustrates why this film must be riffed: http://www.imdb.com/title/tt0086113/board/nest/42537897?ref=ttbd_1
Because this one would make for a great riffing experience.
This movie must be riffed! A Canadian production from Beaver Dam Wisconsin, about a creepy little weener with a Teddy Bear that lures his enemies into a pit full of Trogladites? How can this not be riffed already?
Andrew Kurth commented
oh dear god PLEASE riff this movie. it's a bit creepy at times, but nothing out of the Rifftrax wheelhouse. the teddy voice and the whimsical death scenes alone should be enough to sell this movie, but the little girl's awkward put-down humor takes the cake.