The Eternity Book was ingested by The Thing-That-Cannot-Die who absorbed its magical energy.
Apparently a copy of the Eternity Book along with Sultan Suleiman's scimitar was hidden beneath an ancient Roman temple by Merlin in 1566. The book was later founded by Selma Tolon, who uses its spells as the heroine known as Janissary. Although Tolon has not yet fully master the spell book.
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