Hidden Palace Zone
From Sonic Retro
Hidden Palace Zone is a scrapped level from Sonic the Hedgehog 2. It is an underground zone with purple water, featuring sparkling gems and dinosaur-esque badniks. Hidden Palace Zone is perhaps the most infamous of the scrapped Sonic 2 levels due to its widespread appearance in gaming media before the game was released. The majority of the art in the level was created by Craig Stitt.
Hidden Palace Zone was never completed for the original release; however, a good portion of the first act is playable in the Sonic 2 Nick Arcade prototype and the Sonic 2 Simon Wai prototype. It was one of the first levels to be worked on, however progress stopped early during production. It was nevertheless kept in the game throughout most of Sonic 2's development cycle, with its removal being a last minute decision. This is contrary to Wood Zone and Genocide City Zone, which, culled much sooner, were largely kept a secret.
Notable features of Hidden Palace include green bridges which glow if Sonic or Tails walk on them. This is actually the same object as the bridge in Emerald Hill Zone, but is set to glow if the level number is that of Hidden Palace's. Also featured is a large ramp towards the end of the level, whose collision means it cannot be climbed without positioning Sonic on it with debug mode. Moving up this ramp will lead to the top of the screen, however using debug mode again will show that it continues at the bottom of the level, leading to a bridge covered in waterfalls and inevitably a platform to nowhere.
Unlike other scrapped levels in Sonic 2, Hidden Palace Zone still remains in a corrupted form on the final version of the cartridge, though can only be accessed through game enhancers such as Game Genie. The level plays the unused track 10 in the final game, but opted for the Mystic Cave Zone 2-player music track in the Simon Wai prototype. A second act can also be accessed, but it is a barren version of the first act in all versions of the game. The zone has an icon, intended for the level select screen, but is never seen in normal play. Oddly it does appear in Sonic the Hedgehog 3 however, as this game recycles Sonic 2's level select with minimal alterations.
An interview with Yuji Naka revealed that Hidden Palace Zone was originally intended to be a level where the player would be warped to after collecting the 7 Chaos Emeralds. Once there, they would receive the power to morph into Super Sonic. The idea was ultimately killed and the ability was given to the player immediately. Craig Stitt, in an interview with ICEknight, mentioned that Hidden Palace Zone started as two acts but then switched to a single act before being canceled.
Many parts of the level were once grounds for debate, such as the so called "Master Emerald" which blocks a pipe. In actuality, this was meant to be just a breakable object similar to the ones found in Hill Top Zone and Chemical Plant Zone. The Tails 1-up monitor was once thought to be a sign that the level was a Tails-exclusive zone, though we now know it exists due to art mapping changes.
Some hacks, like Sonic 2 Delta and Sonic 2 Long Version, have attempted to restore the level using the graphics from the prototype version and level map and object data from the graphic-less version in the final release.
Hidden Palace was removed but not forgotten. The name was recycled in Sonic & Knuckles for use in an unrelated level, and some of the background art was re-used in Sonic Spinball's Toxic Caves, also designed by Craig Stitt. Some elements like the glowing bridges and spheres in the background were used later in Sonic 3's IceCap Zone as well. The zone finally was restored 21 years later, as a single-act level in the 2013 remake of Sonic 2.
When Hidden Palace Zone was first made accessible to the public, there was much speculation about the existence of a Tails 1-up monitor at the start of the stage. Sonic 2 was built off Sonic 1, and early in development monitor designations were reassigned. The object subtype number for the Tails 1-up monitor was orignally the object subtype number of a Sonic 1-up monitor. The early Nick Arcade prototype places Tails 1-up monitors in Green Hill Zone where the Sonic monitor should be.
The shield monitor in the beginning was also presumably meant to be a 10 rings monitor, based on the changes in object subtype numbers.
Unlike other scrapped levels, Hidden Palace contained enemies, none of which were seen in the final build of the original game. Some enemies were not given official names. It is also the only level in any of the Mega Drive Sonic games where enemies re-spawn if not on-screen.
The Nick Arcade prototype also includes Stego, another dinosaur badnik which will charge at Sonic and Tails if they come too close.
A number of other badniks are rumoured to have been designed for Hidden Palace:
In the Final Release of Sonic the Hedgehog 2
Hidden Palace is accessible in the final version of Sonic the Hedgehog 2 by using the Game Genie code ACLA-ATD4 (AB6X-ATBR in Knuckles in Sonic 2). From here, enter the Level Select code (19, 65, 09, 17 with in the sound test screen). Go back to the title, and hold + to access the level select screen. Then select Death Egg Zone (Special Stage in Knuckles in Sonic 2).
Almost all of the artwork is gone in the final game, and with this goes collision data, making the zone virtually unplayable without enabling debug mode (1, 9, 9, 2, 1, 1, 2, 4 with at the level select screen). It is impossible to complete the level without placing a capsule with debug mode. All the items in debug mode that you place are from Oil Ocean Zone. "Beating" both acts will take the player to Oil Ocean Zone.
While the Tails monitor object does not grant an extra life in the final, it is, however, fully functional in Knuckles in Sonic 2.
The Sonic the Hedgehog 2 remake for mobile platforms adds Hidden Palace Zone as a bonus 1 Act Zone, courtesy of Taxman and Stealth from Sonic Retro who worked on the project. This level is not in the main level progression, and must be found to access it. The level entrance is located where the dreaded spike pit was located in Mystic Cave Zone. Instead of leading to an inescapable pit of spikes, the pit is now a transition point to Hidden Palace Zone.
The level has been completely reworked using the original assets and sprites from the Sonic 2 Beta. Some similar areas from the original screenshots exist, but the level is mostly a brand new level layout. The music used for this zone is the 2-Player music for Mystic Cave, as was seen in the Simon Wai Prototype. New gimmicks in this completed version include water pipes that blast you through the tubes, and ziplines that thrust you upward using the slanted shafts from the beta. The water slide now works as intended, and the big Emeralds are still breakable objects, now concealing springs. The Redz, BBat, and Stegway (formerly Stego) badniks are here fully functional. Redz can also now breath fire in a small stream from his mouth.
Eggman has a brand new never-before-seen boss machine for this level, which involves using a music device to blast loudly and cause the cave to drop rocks. He also drops bombs into the water, which occasionally will cause a rising column of water intended to hurt Sonic, but can be used to disable Eggman for hits.
The original stage can be accessed through a code on the stage select menu. After entering the debug mode cheat, playing the sounds 03, 03, 03, 0B, 10, 10, 10, 04 and selecting "Hidden Palace" will take the player to the "Proto Palace Zone", which is Hidden Palace's original layout as seen in the Simon Wai prototype. This version of the stage, unlike its revised counterpart, uses Track #10 as its default background music, and the "Master Emerald" acts as a warp that takes the player back to the stage select, rather than being a breakable object.