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By Matt Newman
<yakmir@yahoo.com>
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Tails II
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Hidden Palace in Sonic 2, I believe was designed for Tails only.
The evidence is there:

-First, the most obvious thing, the Tails extra life.
-Also, Hidden Palace does not work in 2 player even with all the 
 screwy things you can do to Sonic 2. Why? Because it was not designed 
 for Sonic to be playable in.
-The emerald. As we all know, nothing happens in Sonic 2 when Tails
 gets all the emeralds. I believe Tails's collection of the emeralds
 WOULD have "activated" the HP Master emerald somehow, enabling
 Super Tails. Well... Super Tails can be got using debug in a 
 Sonic & Tails game, so the character existed...
-The missing Badniks, I believe, were designed as slightly easier 
 Badniks in order to make Tails' game easier (as it is in Sonic 3). 
 These badniks would have been taken out when Sonic was given access
 to Hidden Palace, explaining their lack of appearance in the game
But WHY? You ask. 
This is, I believe, the reason HP is Tails-only: Tails was to have 
 a separate level progression (where Hidden Palace would replace one
 of the harder levels such as Metropolis - the easier Badnik theory is 
 in line with this as the Metropolis badniks are some of the hardest
 in the game.) 
It's possible also that Tails had a completely different storyline, 
 whereby instead of ferrying Sonic through the sky in the plane, he 
 took a more earth-bound (and easier - that theory again!) path to 
 Robotnik, and to an easier Death Egg (Death Egg Act 2, for example - 
 it's in the level select.) Genocide City, as well, could have been
 part of the Tails-only level progression... it could have been Tails'
 second last stage (or even an easier 'city' stage, so the programmers
 could use some of the Metropolis 'city' sprites without giving Tails
 too hard a level.)

So, what happened?
 I believe Tails's level progession was shelved during the beta stage.
 When this occurred, the easy Badniks were removed but Hidden Palace
 was kept in the hope of turning it into a Sonic stage. Construction
 stopped on the level until it could be worked into Sonic's level
 progression, which obviously enough never happened. This would also 
 explain why Genocide City and Death Egg 2 are 'empty', these 
 'Tails-only' zones had just had level data added by the time the 
 Tails level progression was scrapped. 
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Taken from 'Secrets of Sonic the Hedgehog - The Original'
http://secretsonic.cjb.net
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