Hang Castle is one of only two stages that contain the mysterious gravity inversion switch (the other stage being the next stage Mystic Mansion). Its effect in this stage is limited to flipping the stage upside down (though, through hacking is revealed to be teleporting characters to areas identical to an upside-down version of the original). The castle is also filled with booby traps, such as the ghosts that appear, as well as the invisible walkways formed by torches. The Egg Magician/Egg Bishop enemy also debuts here. This robot has two faces with different personalities: on the kind-looking red face, it casts a spell to heal all robots nearby, including itself; the sinister blue face can curse the ground to suck rings from anyone unlucky enough to stumble into it. It will not flip faces of its own accord, but the player can force it do so by creating a tornado in Speed Formation. Because of their unique Light Dash ability, Team Sonic and Team Dark can find trails of rings in this level.
After the second team battle, Team Sonic infiltrates the castle to find Eggman and Shadow. Team Dark enters the castle while Shadow ponders over his identity and what exactly Sonic is. Team Rose finds the haunted castle and continue after Amy reminds Cream and Big of Chocola and Froggy. Team Chaotix are off to find the keys located in the castle (presumably to get into Mystic Mansion).
Collect the keys without being detected by the enemies!
If the Eggman statue is looked at while upside down, a statue of Neo Metal Sonic can be seen, foreshadowing that Eggman isn't the real villain after all. (Seen only in Team Sonic, Team Dark, Team Chaotix and Super Hard Mode versions)
This is the only stage in Sonic Heroes to have two musical tracks: one for when the castle is right-side up and another one for when it's upside down.
If Team Sonic and Team Dark are played during this level and reached the end, while going up towards to the roof of the castle (down if upside down) the moon is shown to have a face with a creepy smile
If Team Sonic and Team Dark are played and start at the beginning of the level, if one pauses on the gap at the beginning, the buildings are shown to be stretched and falling is shown to be a never-ending void if somewhat hacked.
Hacking reveals the Teleport Balls don't invert the level, but warp the characters to a different part of the level made to appear upside-down.