Sorry it's not.
There is no such thing as Sonic Adventure Battle 1, nonetheless no Sonic Adventure is playable on Sonic Mega Collection.
Espio is not playable in that many games. However, he is a playable character in Sonic Hero's. He is an assistant to you in Shadow the Hedgehog, though you can't play as him directly. In Sonic the Fighters (you can find it in Sonic Gems Collection) you can fight as Espio. Those are the only games I know of, but I .
Yes, Sonic CD, Sonic Mega Collection Plus, Sonic Gems, Sonic Heroes, Sonic Adventure DX and Sonic Riders are all playable on PC.
you can in s3&k by beatining lava reef but you have to cheat for sonic 3
Computer, I think SEGA Saturn and if you have Sonic Gems Collection it's playable on Xbox, PS2 and Gamecube.
Hidden Palace is a deleted stage, it can be played in a certain version of Sonic 2 by entering cheats into the sound test. But the level is incomplete and has no exit without one being made with debug mode.
to me it happened after finishing sky chase without using any codes.
Espio is playable in Sonic heroes,Knuckles Chaotix,Sonic the fighters,Shadow the hedgehog and Sonic Rivals 2.
Only Sonic has been a confirmed playable character.
Reala isnt playable in any sonic games, maybe a cameo but not playable
just sonic.
Shadow from Sonic is not playable in Super Smash Brothers Brawl. The only playable character from the Sonic franchise in Super Smash Brothers Brawl is Sonic himself.