Hidden Palace Zone (InstanceTopic, 23)
From Compile Worlds
The Hidden Palace Zone is a zone found in the Sonic 2 Beta, which is for the most part playable. However, there are several problems with the zone. Both acts are the same, there is an impassable part half-way through the act, and it cuts off without an end level signpost or boss. This renders the zone unbeatable without debug mode or hacking.
Music
Supposedly, the background music for this stage was to be track $10 in the final game's sound test. However, in the beta, the Mystic Cave Zone two-player track plays. This may mean that the song was intended to be the Hidden Palace song at one point, but it could just as easily have been a mere placeholder until track $10 was composed and programmed into the game.
In Sonic 2 Beta
In the Sonic 2 Beta, all of the layout for both acts is complete and fully functional. The object data also seems to be mostly complete, as enemies and even awesome bridges that glow when you walk on them are in the zone, functioning as they should. However, the pipes do not work correctly, and they need to be gotten through with debug mode. However, in one awesome Sonic 2 hack that Chao once played, the Hidden Palace zone was the first zone, and the hacker had fixed all the shortcomings, including adding signposts and capsules and making the pipes work.
No... can that be the Master Emerald?!
Of course not, silly. SEGA isn't going to put all of their good ideas in one game, you know. Anyhow, the "Master Emerald" you see in this zone is simply a fancy pipe stopper, blocking entrance into the non-functional pipe it covers.
OMGWTFBBQ Tails monitor!!1
Yes, all of the 1-ups in the stage feature Tails' face instead of Sonic the Hedgehog's. The programmers just left their object data offset reference sheets at home that day.
However, some fucked up people are insane and believe that the whole damn zone means Tails was supposed to be the guardian of the Master Emerald. However, we all know it isn't true, and we all know SEGA would never give Tails such a significant role in a plot, despite our wettest dreams.
In the final Sonic 2
According to the famous Yuji Naka, Hidden Palace was one of the last zones to be cut from the game. However, clever Game Genie and Action Replay hackers have discover that the stage and it's layout in fact DO STILL EXIST IN THE ROM. However, what they did delete was the Graphics data, making it look like an absolute mess (worse than even Genocide City or the early Death Egg). So don't use the code unless you plan on restoring the Graphics data or know the layout of both acts by heart. And even if you know the layout, you'd better be prepared to get pissed off, because the collision data is all FUBAR anyway.