Complex sentence: When Shrek arrives, he helps disarm the Fairy Godmother of her wand, before Charming forcibly kisses Fiona, believing the potion has taken effect, but Fiona temporarily knocks him out with a headbutt.
Split into simpler sentences: When Shrek arrives, he helps disarm the Fairy Godmother of her wand. Charming then forcibly kisses Fiona, believing the potion has taken effect, but Fiona temporarily knocks him out with a headbutt.