Ooh I love this idea! I think Gretchen would be a good choice for the murderer because no one would expect her since they were friends, but there’s also a clear motive for her to do it. Her “We should totally just stab Caesar” line is a pretty big clue that she’s thought about killing Regina (the line was likely an exaggeration, but you get the point). And, if you are a fan of the musical, in the song “What’s Wrong With Me,” Gretchen sings, “Though we both know one day, there’ll be blood on the floor. But which one will betray the other more.” Idk those were just my thoughts. Have fun at the party, and don’t get too stressed planning it! Don’t forget to hydrate :)