Complex sentence: David explains the continuing war of the Red Knight against the evil forces of the Ash King and his army, and that he caught the scent of their arrival, which mimicked the arrival of a previously three (from the outer world) years ago.
Split into simpler sentences: David explains the continuing war of the Red Knight against the evil forces of the Ash King and his army. He caught the scent of their arrival, which mimicked the arrival of a previously three (from the outer world) years ago.