Complex sentence: As Goku and Hirudegarn battle, Trunks intervenes and cuts Hirudegarn's tail off with Tapion's sword, Goku soon realizes that strong emotions drains Hirudgarn's energy and he angers the monster up to a point his defensive armor is useless.
Split into simpler sentences: As Goku and Hirudegarn battle, Trunks intervenes and cuts Hirudegarn's tail off with Tapion's sword, Goku soon realizes that intense emotions drain Hirudgarn's energy. So he angers the monster up to a point his defensive armor is useless.