Complex sentence: Sassy, who has the fictional name Wiki in the book, is a lost kitten adopted by a mother cat with two kittens of her own and attempts to be accepted by his adoptive siblings by performing acrobatic tricks.
Split into simpler sentences: Sassy, who has the fictional name Wiki in the book, is a lost kitten adopted by a mother cat with two kittens of her own. He attempts to be accepted by his adoptive siblings by performing acrobatic tricks.