Complex sentence: One day out of every century, as the forces of good and evil reach a balance, the otherwise-indestructible amulet becomes vulnerable to destruction, and the next day of balance falls within a couple days, at the stroke of midnight.
Split into simpler sentences: One day out of every century, as the forces of good and evil reach a balance, the otherwise-indestructible amulet becomes vulnerable to destruction. The next day of balance falls within a couple days, at the stroke of midnight.