The rules of the variants are not explained through the campaign so you have to play and guess as you go, I tried to make each new level surprising in its own way :)
The idea came to me because along the years I've seen a surprising number of Tic Tac Toe custom rules and thought it would be cool to make a whole game out of it. I settled on 20 levels but have a ton more ideas and I'll probably add some in later updates.
Surprisingly to me the hardest part was publishing an app on the App Store and Play Store (still pending because it requires 12 testers), the whole process was pretty nightmarish. At least I had a lot of fun making the game itself!