I appreciate the kind words! And thank you for playing.
For the alternate ending, you need to finish two optional chapters (after 11 and 13), as well as either finishing the optional chapter after 16 or collecting an item in chapter 20 that spawns if you didn't go to that particular bonus chapter. The optional chapters are named "The Amber Swan", "The Crystal Swan", and "The Crimson Swan".
Also, feel free to share thoughts on balance. If things are too hard, too easy, and all that jazz.