Cool game and a really cool idea to combine the two mechanics! Here is some feedback of things which might even improve the experience:
- Maybe at some point I would stop bringing in new balls. Or at least slow down the spawn rate for the new balls. In this way you can concentrate more on combining these balls. With the current spawn rate I was very busy to avoid not too lose many lives and could not concentrate at all on the combining mechanism.
- The sound effects and music could maybe be improved a bit. The music is very short and for the flipper I would use a more clicky sound.
- Maybe an additional game mode with unlimited lives and time would be fun. Just for a more casual game experience.
Still, this is a very cool entry and I had fun playing it. Well done!