Complex sentence: It seems that Morgana has prevailed, but she forgets agout her Dark Stone, which has been picked up by Gwenevere, who, aided by their friends, manages to fuse the Dark Stone with the Sun Stone.
Split into simpler sentences: It seems that Morgana has prevailed, but she forgets about her own Dark Stone, which has been picked up by Gwenevere. The princess, aided by their friends, manages to fuse the Dark Stone with the Sun Stone.