Fun little game with a neat core idea.
To make buff more useful. Could it be allowed to choose column or row when you are only filling in one square? After I had used it, I only had one row left to fill, so I didn't benefit from it.
The x in multipliers are usually written after the number. I especially got confused by the x-3.0. It looks like it will be the number of squares minus three rather than multiplied by minus three.