It's (basically) a rule that Twenty One Pilots doesn't write in the same genre twice. And we can definitely hear that here with "Heathens." The song is part grunge, maybe part R&B, and part pop. It reminds me of "Fairly Local" more than any other song by them, but even then it's iffy. You can listen if you like and let me know what you think (unless the leaked location I've been listening to has already been removed). Alternatively, I recommend searching for it on Twitter; there seem to be many uploads of the song there.