Complex sentence: Agatha Harkness was first introduced as Franklin Richards' governess after she easily fended off the Frightful Four when they came to abduct Franklin Richards and admitting to the Fantastic Four that she is a witch.
Split into simpler sentences: Agatha Harkness was first introduced as Franklin Richards' governess. She easily fended off the Frightful Four when they came to abduct Franklin Richards, and admitted to the Fantastic Four that she is a witch.