Great concept and game! I especially liked the digit-flipping one; that one was a very nice touch. The twist at the end was nice too. Level 7 was tricky; at first I did this:
738 512 64
the logic being that the 3-1-4 and 5-1-2 add to eight (ATE) and the 8-2 and 6-4 add to TEN. I was definitely overthinking it, but there’s a puzzle there somehow. I’m glad that there was a challenge even for people like me who can do small sliding puzzles somewhat quickly.