Complex sentence: Gawain is now free to defend himself from further harm and seizes his sword, helmet and shield, but the Green Knight, laughing, reveals himself to be the lord of the castle, Bertilak de Hautdesert, transformed by magic.
Split into simpler sentences: Gawain is now free to defend himself from further harm. He seizes his sword, helmet and shield, but the Green Knight, laughing, reveals himself to be the lord of the castle, Bertilak de Hautdesert, transformed by magic.