Complex sentence: Bill enters the monster's mind through the Ritual of Chüd and discovers It's true form in a mass of floating orange light (or "deadlights"), which he repels, and the Losers swear a blood oath to return to Derry if It resurfaces.
Split into simpler sentences: Bill enters the monster's mind through the Ritual of Chüd and discovers It's true form is a mass of floating orange light (or "deadlights"), which he repels. The Losers swear a blood oath to return to Derry if It resurfaces.