So the Hidden Palace is doing what they call Sonic month, where they are dumping a LOT of protos.
They started off with Sonic CD ones, the earliest one is dated December 4th 1992. Palmtree Panic is the only level available, and it was known as "Salad Plains". It's also the only build to ever reference the unused R2 zone, but of course doesn't feature anything other than Salad Plain.
It was followed by Sonic Chaos dumps.
Next they moved onto Sonic 2. The first beta they showed was just before the CENSOR prototype that was dumped earlier. This one is dated Sept 14th 1992. Most notable is that Hidden Palace was in the process of being removed, but not fully. Also the first build that had Sky Chase, Sky Fortress, Death Egg and a special stage. It also confirms that Mystic Cave was Dust Hill Zone, as it was given a title card in this build.
https://hiddenpalace.org/Sonic_the_Hedgehog_2_(Sep_14,_1992_prototype)
Yesterday they showed off another, this one dated August 21st 1992. Wood Zone and Hidden Palace are still fully intact! Though it's disappointing that they are identical to the Wai builds, it shows how long they survived. I didn't expect Hidden Palace to get anything more, but I thought that Wood might have gotten more of it's level layout. Hidden Palace still uses the Mystic Cave 2p theme as well, even though sound 10 is implemented.
Casino Night is also it's former pink self, with a completed layout and a boss battle. There are no other objects, though.
https://hiddenpalace.org/Sonic_the_Hedgehog_2_(Aug_21,_1992_prototype)
They promised one last prototype to be shown off in a livestream on Saturday at 2pm pacific. They didn't specify what game it was for, but it's something you don't want to miss.