The Demon is killed through Zakk's self-sacrifice, though only Brodie and Medina survive the battle. They are shown as a happy couple two months later. Brodie also hears Zakk's voice through a record and Zakk tells Brodie he is having a great time in Hell (alongside many musical legends).

Long Ending:
Brodie (Milo Cawthorne) moves to a small New Zealand town to live with his relatives after his mother is arrested. Brodie is into metal music, which his new family abhors. His cousin is the school's bully and causes Brodie to be ostracized. His only friends are Giles (Daniel Cresswell) and Dion (Sam Berkley), the Dungeons and Dragons-playing nerds at his high school. He soon meets a delinquent metal-head named Zakk (James Blake) and the pair bond over their shared musical tastes. The four start a band, but Brodie often fails to complete his guitar solos due to a lack of self-confidence.

Zakk convinces Brodie to break into a home where it is rumored that a former metal legend is living. They find the rock star, who accuses them of being occultists. At that same time, actual occultists break into the house. The rock star gives the boys a record and tells them to run. The occultists then kill the rock star. Inside the record sleeve, the teens find some ancient sheet music and words written in Latin. The band tries to play the music, but Brodie keeps bumbling over the guitar track. Unbeknownst to them, each time they attempt to play the song, everyone within earshot starts getting possessed by demons (although the possession fails each time Brodie fails to play the solo)

Brodie begins getting closer to his cousin's ex-girlfriend Medina (Kimberley Crossman) and is beaten up by his cousin as a result. Medina asks Zakk to give Brodie a note asking him to meet her in the park one night. Zakk never gives Brodie the note and goes to meet Medina instead, claiming Brodie isn't interested (though he knows Brodie is crazy for her). He uses the opportunity to make out with Medina himself. Brodie translates the Latin and sees it is a spell for summoning a Demon that will gift him with wealth and power. Desiring such things, Brodie finally manages to play the guitar part with his band. Everyone in the town who hears the song becomes fully possessed by demons, including Zakk's dad and Brodie's aunt and uncle. Zakk and Brodie go to see a psychic who tells them that the Demon will arrive himself by 3:00 AM to possess the most immoral person in town and lead his possessed minions to invade the world. She is killed by the possessed townspeople before she can explain how to reverse the curse. Meanwhile, the occultists arrive in town. The leader of the cult is killed by his underling Shanna, who wishes for the Demon to possess her instead of the leader. They begin working with the possessed to find Brodie.

Zakk destroys a note left by Giles and Dion to meet them and Medina (who saved their lives from an attack) at the school and tries to convince Brodie to leave the town to rot (literally) in Hell. Brodie refuses to do so and Zakk reluctantly agrees to stay and help. They theorize that if they play the song backwards by 3:00, they will reverse the possessions and stop the Demon's arrival. The pair eventually reunite with Giles, Dion and Medina and all of Zakk's deceptions are exposed. He and Brodie fight and Zakk decides to leave after beating up Brodie. The occultists then capture the four remaining teens and destroys the sheet music.

Zakk eventually returns and rescues his friends (and he and Brodie patch things up). The band attempts to play the song backwards from memory, but Giles and Dion are killed before they can finish. The Demon begins possessing Shanna, but Zakk kills her before his arrival is complete. The Demon instead possesses Zakk (the most immoral person remaining), but Brodie plays a guitar solo so perfectly that it gives Zakk the strength to temporarily retake control of his body. While in control of himself, Zakk convinces Brodie to kill him. Doing so saves the day and sends the Demon back to Hell.

Two months later, we see Brodie and Medina living happily together as a couple and both are still fans of heavy metal music. After the credits, Brodie is listening to a record when he hears Zakk contacting him from Hell. Zakk explains that he enjoys Hell as he gets to hang out with plenty of dead music legends like Ronnie James Dio and Kurt Cobain, as well as some living musicians like Paul McCartney.

Order of Deaths:

Thanks Evan B!