Annoyingly difficult. My max is 10. There are times where two balls about to hit fire at the same time in opposite sides, that is guaranteed lose. I do not like how we lose once a ball hit the fire. Good concept and good theme application though.
I see the potential to expand this. Firstly, you can be forgiven from one mistake - have 3 life at least. The opponent does not have to be hit 12 times anymore, it can be less or more. When the clock balls ran out, it will be refilled. Some balls can have special effects embedded in them making them behave a bit differently: ice ball - freezes the green paddles it hit, mushroom ball - enlarge the target yellow paddle when caught, etc.