At around 18:33, you can see April, Derek, and Ben stealing Ann's skeleton after saying goodbye. It is safe to assume that Ann herself stole it from the hospital she works at. The current whereabouts of the skeleton are unknown.
Ron Swanson dresses as a pirate for Halloween. Nick Offerman, who plays Ron, is the voice of a pirate in The Lego Movie (2014) which also stars Chris Pratt (Andy).
Leslie Knope says "Let him go, stay on the leader!" perhaps inadvertently referencing a line Darth Vader says in Star Wars: Episode IV - A New Hope (1977).