Complex sentence: The "Darkhold" s power is so vast it took the combined strength and will of both Merlin and St. Brendan to contain it, and even together, they were unable to destroy it or its power.
Split into simpler sentences: The "Darkhold" s power is so vast it took the combined strength and will of both Merlin and St. Brendan to contain it. Even together, they were unable to destroy it or its power.