As I followed along with the lesson, I noticed a couple details that were missing:
1. The Sprite's `scale` needs to be adjusted down to 0.24 as seen in the final code.
2. The "_idle" animation isn't defined, but it is used in the `set_is_selected()` function.
3. If you are following along with the lesson you'll get an error after writing the first example of the `Unit` class. This is because that example defines the `_set_is_walking` function without defining the `_is_walking_var`. The completed code sample eventually does add the variable though.
Will be fixed in the next update, thanks!