A brief summary of how the Gates of Hell were opened:

Tumblr user ChaosControlled123 has transcribed a piece of music written on the butt of a guy being tortured in hell from an medieval painting.

It appears that the university student named Amelia is the first person to ever actually attempt to play the song.

Most likely, this has summoned Satan and he will unleash his band of hellbeasts and succubi to torture us in the last of our mortal days.