So this scene takes places after The Joker and the Batman fight for the last time (Fight where the Joker sicks dogs on Batman in that unfinished building) and before the final scene in which Harvey is thinking of killing Gordon and his family.
"I think you and I are destined to this forever." Walpurgis Night said while dangling upside down.
"Why so serious?" W.N. said with a troll face.