So, many people are aware of Mr. Fixer's "Dual Crowbars" chaining with Setback's "Friendly Fire" to just keep punching enemies until Setback dies. There have been some suggested tricks for keeping Setback alive (a good Silver Lining, Fixed Point, etc.) I think I have found the one that makes damage infinite while being relatively easy to set up.
You need four heroes - Mr. Fixer, Setback, XTreme Haka, and anyone who can give damage reduction. Captain Cosmic or Argent Adept is probably easiest. It is also useful to have a fifth hero who can provide decent card draw, but not technically necessary (Adept is valuable here too, since he can give card draw while setting up the loop.) If you're cautious, you can actually drop the whole loop in a single turn.
Your one-turn setup looks like this:
1. Haka plays Ta Moko and uses Die Hard to shield Setback.
2. Setback plays Friendly Fire.
3. Give Haka an extra 1 DR via something like Counterpoint Bulwark or Energy Bracer (alternatively, with the right setup you can give Haka 2 DR in this step and he won't need Ta Moko at all.)
4. Mr. Fixer plays Dual Crowbars and then Strikes an enemy.
When this happens, as in the usual combo, Fixer will attempt to do 3 damage to Setback via Friendly Fire. This will redirect the damage to Haka and reduce it to 1. Haka will then heal 1 HP. Since he successfully did 1 damage, Fixer will then do 2 damage to an enemy. He will then hit Setback via Friendly Fire...
So it's basically the same loop that usually kills Setback, except that because Haka heals 1 HP every time he gets hit, he won't ever actually run out of health, and since he's still taking damage, it will loop out to the villain. Infinite punches, wiping the board clear of foes.
Note: If your enemy has more than 1 DR, this plan will not work. You can't make Fixer's damage irreducible or else he will kill Haka. If your enemy only has 1 DR, you will still do infinite damage. For every extra DR they have, you'll need to find a way to stick one more DR onto Haka and one more damage onto Fixer.