I also owned a C64 back in the 80s. I used to enjoy playing on it, and I also wrote a number of programs. One of them was a simple implementation of the old sliding piece puzzle, with letters. It was a 4 x 4 grid, with a random selection of 15 out of 26 letters, and I programmed it so that it would save the moves it made to jumble the letters up, thereby enabling it to show the solution if you ran out of time or moves. 9 levels, a simple tune that played if you won, another tune if you lost, and the sound of a ticking clock, together with a constantly updating display completed the game. And it was all in BASIC. No machine code or assembly language was used. I wish I had published that game, as I used to get magazines where you could send in user-submissions.