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The East Balcony is an area in Treacherous Mansion in Luigi's Mansion: Dark Moon. It is accessible via the south door in the East Corridor and east door in the Jungle Exhibit, the area is a sort of outside courtyard with numerous plants and gargoyles.
The area is divided into two sections. The one accessible via the East Corridor brings Luigi around the outside of the building, whereas the other section (entered from the top floor of the Jungle Exhibit) leads into a closed off area with multiple golden frogs as enemies and a treasure chest. There's also an opening in which Luigi can look through to see the frogs and treasure chest.
The East Balcony is optional in all missions, being first explorable in A Train to Catch.