Complex sentence: Afterwards, Isaac realized his quill and ink were missing, so he pays a visit to see Cruella and is stunned that she used him as Cruella uses the skin from her mother's dogs as fur for her signature coat.
Split into simpler sentences: Afterwards, Isaac realized his quill and ink were missing, so he pays a visit to see Cruella and is stunned that she used him. Cruella would later use the skin from her mother's dogs as fur for her signature coat.