Couple of ways of creating a cutscene for a GM:S game, but I haven't found an extension specifically for that purpose till date. There are two easy approaches that you could go for: First, create the cutscene with a third party tool and play the video produced with the help of an extension (there are a number of extensions to play videos on the Marketplace). Second, use a timeline and create a cutscene mid-game with the help of objects. ^^'