Any power combo can be good if the user is good with both of them. It depends on the user, not the power. I could become insanely overpowered if I had Bubble Manipulation and Salt Manipulation and mastered them to the highest degree.

I just want them to complement each other

Gas Manipulation and Elasticity aren’t very compatible, but it’s unique which I find is more important.

I know what you mean I’ll just have to make them compatible

Flubber was really good show