The hidden character needs 5 emblems then you will unlock a hidden level and then you would need to beat the hidden level to unlock the hidden
also another character called fang would be able to bounce on breakeble floors and break them Metal sonic can break breakable walls but you need to be in his sprint mode and you need to keep his speed to due it or else if you bump in to wall or if you slowed down.
there are also modedfied characters that can do the same as the vanilla characters.