you HAVE to complete the subspace emissionary and then there are two choices, go to the cavern of the subspace emissionary and go through a certain door, and there is another which is complete boss battles ( any level ) with fox or falco.
Depending on how you unlock them, possibly.
if you mean by: can you unlock any more secret caracters in brawl? then i dont think so.
play 450 brawls
After you beat Subspace Emissary, go back to "The Ruins" and when you find a floating door go in it and fight wolf and defeat him to unlock him
wolf, foxes rival
Use story mode.
It depends on you usually it will be jigglypuff.
play 400 brawls.
get him on sse or play 450 offline maches
You can get Jigglypuff, Wolf, and unlock Sonic the instant you are done.
Wolf. You can only unlock him in brawl.
you can't unlock him in super brawl summer you only unlock him in super fall brawl