Complex sentence: Raiden soon discovered that Shinnok had gained access to the realm through the powers of a mystical amulet, which permitted the user to enter without challenge and keep the other Elder Gods from intervening.
Split into simpler sentences: Raiden soon discovered that Shinnok entered the realm through the powers of a mystical amulet. It allowed Shinnok to enter the realm without challenge and keep the other Elder Gods from intervening.