Castle Siege
The Castle is a stage seen in the SSBB trailers. It has not yet been officialy confirmed, but appears in many trailers and screenshots. Its name and series are unknown, though it resembles something that would be found in a Zelda or Fire Emblem game.
Rumours say it might be a Fire Emblem stage, as castles in Hyrule have never been attacked with catapults, like this stage was in a trailer. Both the battle outside of the castle and the inner sanctum appear very similar to Dolua Castle from Fire Emblem: Ankoku Ryū to Hikari no Tsurugi and Fire Emblem: Monshō no Nazo.
Like the Helipad stage, this stage appears to have both an exterior and an interior, of which the connection is unknown. They could be seperate stages, or they could be one and the same. For simplicity, they are currently regarded as the same. The exterior has been shown to be attacked by flaming arrows and catapults, which will presumably act as hazards.