I've got 8 remaining. I'm working on Ghost Rider. I've found the best way to toughen up a new character that you haven't been using is to play the Ulik board. There are limitless enemies and you just work them over and earn a shitload of coins. You can also gain levels pretty fast. I take the new guy, like Dr. Strange or Elektra and put them with Thor, Wolverine, and Moon Knight. Moon Knight has a great Extreme attack. The bruisers help keep the new chump from getting wasted.