Complex sentence: Alphamon is a fictional character from the Digimon franchise, the Mega form of Dorumon, a Digimon of great power of the "Alpha-Gain-Force".
Split into simpler sentences: Alphamon is a fictional character from the Digimon franchise, the Mega form of Dorumon. He is a digimon of great power due to his possession of the "Alpha-Gain-Force".