Complex sentence: Beyond the Wall, the White Walker army arrive at Eastwatch, along with the Night King riding on his wight dragon, Viserion, who begins burning the wall to the ground, allowing the dead to pass into Westeros.
Split into simpler sentences: Beyond the Wall, the White Walker army arrive at Eastwatch. Along with the Night King riding on his wight dragon, Viserion, who begins burning the wall to the ground, allowing the dead to pass into Westeros.