Twenty One Pilots have shared a mash-up of the Stranger Things theme tune and their 2016 song ‘Heathens’ – check out the performance below.The Ohio duo – comprising Tyler Joseph and Josh Dun – were playing a headline set at the Electric Castle festival in Romania last Friday (July 15) when they paid homage to the Netflix sci-fi series.To introduce their 19-track set, the band aired a montage of pivotal scenes from Stranger Things 4 on the big screen behind the stage. It showed Max (portrayed by Sadie Sink) being tormented by the sinister villain Vecna (Jamie Campbell Bower).The video was soundtracked by Kyle Dixon and Michael Stein’s official theme tune for the show.