Complex sentence: He plays a relatively minor role during most of the game, but during Ending A and C, when the dragons attack the human population, he uses his pact partner to summon an army of Golems to destroy them.
Split into simpler sentences: He plays a relatively minor role during most of the game. However, during Endings A and C, when the dragons attack the human population, he uses his pact partner to summon an army of Golems to destroy them.