There are 4 episodes Sonic, Shadow, Silver and Last, you unlock Shadow by encountering Shadow in story mode, and Silver's story is unlocked by encountering Silver in Sonic's story, last story is unlocked by beating all 3 hedgehog's stories, none of these are 'hidden' per say, but there the only episodes or stories in the game.
Beat all episodes and you'll unlock a 4th episode called "last episode" where you have to be Super Sonic, Super Shadow, And Super Silver.
No episode in all the sonic the hedgehog shows does it show sonic the hedgehog's feet
No.
the first episode of sonic x
Finish Crisis City to unlock Shadow the Hedgehog's story.
Complete Sonic's Crisis City.
Sonic the Hedgehog 4: Episode 2
While a second player can control Tails like in Sonic the Hedgehog 2 and 3, you cannot play as Tails alone in Sonic the Hedgehog 4 Episode 2.
In Sonic SatAM they kiss at the end of the final episode, "The Doomsday Project"
Episode 38
No information regarding the release date of Sonic the Hedgehog 4 Episode 2 has been released by SEGA.
Its episode number 24, how to catch a Hedgehog