

Mario-> Sonic -> Bayonetta -> Little Mac -> Ike-> etc.

The unlocking order can be visualized through this method: The second Classic Mode run does not have to be done with Mario, but can be completed with Sonic in order to face Bayonetta, and, if a player defeats Bayonetta with either Mario or Sonic, she will be added to the roster. If the player defeats Sonic, then he is permanently on their roster. Let's examine Mario's unlock tree: If a player completes a Classic Mode run with Mario, that player will have the chance to battle Sonic as their challenger. The Classic Mode unlock order may be a bit confusing at first but it becomes incredibly digestible upon examination.
