Dies Irae, is a medieval Latin melody known for it's use in the Requiem (Funeral Mass), and means "Day of Wrath." It pops up in the soundtracks of Star Wars, Lord of the Rings, The Shining, Nightmare Before Christmas, amongst many other films, and can be heard in the 4th season of Escape the Night.
This video from Vox does a great job of explaining the history of this tune, and where you can hear it.
So where in Escape the Night can you hear Dies Irae? It can be found in the theme for "The Sword of All Legends". See if you can hear it below.