This is a fun game! It taught me about the alt-key shortcut for managing handles. In Inkscape I just go back and do that with buttons in the UI, so this will save me some time.
On a side note, I don't think this game will necessarily make a player overall better at using the pen tool. This is more like "how to cheat at the pen tool" to achieve an approximation of a stroke with the fewest nodes possible. While playing, I had some pretty ugly-looking Bézier paths that technically passed the test and used fewer nodes than I had available. But, some of the places where the original image had sharp corners were really round on mine.
On a side note, I don't think this game will necessarily make a player overall better at using the pen tool. This is more like "how to cheat at the pen tool" to achieve an approximation of a stroke with the fewest nodes possible. While playing, I had some pretty ugly-looking Bézier paths that technically passed the test and used fewer nodes than I had available. But, some of the places where the original image had sharp corners were really round on mine.