I felt like the difficulty curve was a little off. Some of the earlier levels were harder than the final ones. Maybe you should expand the grid, so the later levels have more possible spots to put the operators in.
Can you please add an auto-repeat option for rival fights? It's really annoying when I know that I can beat a rival with a bit of luck, but have to click twice (accept lost duel and start a new one) every single time.
Not much thought required, since there is really only ever one way to go. Would be nice if there were multiple ways to choose or more complicated puzzles and possibly even a few useless objects to confuse the player and make him think for a bit.
I'd appreciate the option to change one of your custom cards for anything between 1-3 coins. I noticed a little bit too late that my custom answer doesn't really work well with 99 % of the questions. So instead of buying a new card and just not using the old one ever again, I would be glad to have the possibility to change it. Also helpful with accidental typos etc.
 "Math In Grid"){kind=icon}
 "Sword Fight"){kind=icon}
 "Down is Up"){kind=icon}
 "Idle Recruit"){kind=icon}
 "Suck My Card CCG"){kind=icon}
Thanks for pointing this out. At the very least I can add retry button to the pop-up.