Complex sentence: Jubei manages to escape, but Gemma grabs his foot, only to get his arm cut off and falls down to the depths, unable to cause any harm in his solid prison on the bottom of the Japanese sea.
Split into simpler sentences: Jubei manages to escape, but Gemma grabs his foot, only to get his arm cutten off and falling down to the depths. Now unable to cause any harm in his solid prison on the bottom of the Japanese sea.