As you beat the single player mode, you'll slowly begin unlocking the rest of the characters, except for the final boss. (hardcoregaming101.net)
Instead, you can play the first three stages for free, and then you have to make a one - time $ 10 purchase to unlock the rest of the game's content. (venturebeat.com)
While character and item transfers fail to maintain the momentum of «simply unlock the rest of the game now to keep playing,» they do work wonderfully when it comes to giving players a reason to progress to the full game. (kotaku.com)