Complex sentence: Just as Taichi is cornered, his Digivice shines and his old partner Agumon appears while digivolving into Greymon to fight the stronger Kuwagamon.
Split into simpler sentences: Just as Taichi is cornered, his Digivice shines and his old partner Agumon appears. Agumon digivolves into Greymon to fight the stronger Kuwagamon.