Complex sentence: Since then, Submarimon was a valuable fighter during the Digimon Emperor's reign of terror.He transported Cody Hida, spying on the Emperor's aircraft.Once Ken renounced his evil persona, Submarimon was no longer needed and appeared only a few times as Ankylomon was used more.
Split into simpler sentences: Since then, Submarimon was a valuable fighter during the Digimon Emperor's reign of terror. But once Ken renounced his evil persona, Submarimon was no longer needed and appeared only a few times as Ankylomon was used more.