The 2013 iOS/Android phone rerelease of Sonic 2 re-adds the once lost Hidden Palace level. It consists of one act, retains the unused dinosaur and bat Badniks with a few changes, introduces a new jellyfish Badnik and a new Robotnik boss at the end. The 2P Mystic Cave zone music plays in this level.

The entrance to Hidden Palace is found at the bottom of a once-infamous shaft in the Mystic Cave Zone. Originally the shaft had spikes at the bottom that could easily (and slowly) kill the player whether or not they were Super Sonic. The rerelease removes the spikes, thus falling into this hole now takes the player to Hidden Palace.