The quest item for the History of Colonel Pete quest is located in this area. It can be found behind the toon wall towards the back of the staircase in the center of the main room. It must be retrieved before the staircase is raised, otherwise, it's rendered unobtainable and the quest will be failed.
Upon entering this area, Mickey is tasked with freeing a ghost from a bottle. He can be freed by dropping an anvil on one of the pressure plates near the front of the ghost's cell and standing on the other. Once the gate opens, Screeching Sam can be freed by using the spin move on the vase. Mickey is then tasked with painting in the missing halves of two skulls mounted on the walls. Each of the skulls are guarded by Spladooshes in small rooms that can be found by thinning toon walls and floors. After both skulls are painted in, talking to Sam will cause the staircase to raise and the gate to open on the balcony, giving Mickey access to the Haunted House projector screen and allowing him to progress.
Method 2 (Shortcut)
Alternatively, freeing Gremlin Haig provides an opportunity to skip over most of this area. He's trapped behind the Blot painting on the wall and can be freed by thinning it and entering the secret room. Once freed, he fixes the pressure pad. Stepping on it will cause the exit gate to open, but only for 10 seconds. To take advantage of this shortcut, Mickey must make his way towards and through the exit gate before the timer runs out, otherwise, he must complete the area the normal way by rescuing Screeching Sam.