Complex sentence: Myrtle tells her guests that she gave them melon balls laced with monkshood, which made them into "human statues," and revealing that she didn't invite them to chastise them, but to help out the coven.
Split into simpler sentences: Myrtle tells her guests that she gave them monkshood, which made them into "human statues". She tells them that she didn't invite them to chastise them, but to help out the coven.