"Magna Insomnia" is the final boss theme of Final Fantasy XV. It plays during the climactic fight between Noctis Lucis Caelum and Ardyn Izunia. It mixes arrangements of "Somnus" and "Ardyn". The theme was composed by Yoko Shimomura and arranged by Yoko Shimomura and Shota Nakama. "Magna Insomnia" is comprised of three separate movements that play during each of the final battle's three phases. Its first movement is later reused during the "Kingly Clash" in Final Fantasy XV: Episode Ardyn, owing to it being an alternate take on the final battle.
Magna is Latin for "great".
Insomnia is derived from the Latin word insomnis, which means "sleepless." It is the name of a sleep disorder that prevents one from falling asleep or remaining asleep as long as desired. Insomnia is the name of the crown city of Lucis where the final battle takes place.