Complex sentence: Charmeleon evolved when Ash summoned him for protection from wild prehistoric Pokémon; when an Aerodactyl attacked him and carried Ash off, Charmeleon evolved only to fight the Aerodactyl more effectively with Ash's rescue a second priority.
Split into simpler sentences: Charmeleon evolved when Ash summoned him for protection from wild prehistoric Pokémon. When an Aerodactyl attacked him and carried Ash off, Charmeleon evolved only to fight the Aerodactyl more effectively with Ash's rescue a second priority.