I got the season pass on steam
the season pass don't give extra playable Character those DLC are completly separated from the season Pass. And if you got the game not on steam or not retail pre-order you will not recive the extra character ,i mean site where you buy the key(by reciving only the serial to be register on steam) only for lower price those are not "cosider" pre-order, if is this you situation you will not get the Mechromander char.
Instead if you did buy the game on steam/retail during the pre-order period you shoud have the "premier club" to be sure if you have that go in the main menu of the game and go in the Download Content and check if you have other "DLC" excluding the season pass.