I have not yet gotten a chance to play the new Doom video game, but now I have to.
Imgur user TomButcher recently found that at least one tune in the the game's soundtrack, Cyberdemon, shows hidden pentagrams and the infamous "number of the beast" – 666 – when the music's frequencies are displayed through a spectogram, as viewed above.
That means the music spells out 666 and displays many pentagrams.
The dude who wrote the soundtrack, Mick Gordon, recently teased that hidden demonic imagery was somewhere in the game's soundtrack in a YouTube video (around the 3:29 mark), and confirmed the existence of the evil easter egg on Twitter.
The game also references Terminator 2 in another easter egg, which can be seen when a player jumps into molten lava and submerges to his death while giving a thumbs up.
Notice any others?