This for those who love old horror movies. The Curse of the Demon was pretty scary. Devil worshippers give you a cursed parchment. If you don't pass it on before a deadline, a giant demon (maybe 30 ish feet high) appears and rips you to shreds.

Let's say the MCU Avengers and DCU JLA members each get a parchment. They don't know about the curse to pass it on. The demon appears, who can resist it? The demon never faced an opposition in the movie, it just ripped humans to shreds. It can follow you anywhere.