Use the magic whistle, and play Mastermind/Wordle with the letters A, B, C, D, E, F, and G to spell words that will break the spells on the transformed monarchs:
When you return to the King of Birds, and he asks what caused all these transformations, recall how several of the monarchs had recently eaten leafy green vegetables. The answer is CABBAGE.
I started making this for the HEX prompt. I wanted to make a Little Match Girl game where she met the Queen of Vampires (because Atë may soon show up in another Little Match Girl game...) and HEX seemed like a good candidate.
Every Little Match Girl game is supposed to be based (however distantly) on a specific Hans Christian Andersen story. I searched for Andersen stories that involved "curses" and "spells" and found "The Marsh King's Daughter," which I had not read before. I read it.
It is so bonkers. I absolutely adore this guy. What struck me about this story, among other things, was the abundance of incongruent characters: Fairies, storks, Vikings, an enigmatic Marsh King... And incongruency is essential for a Little Match Girl story, so this is perfect. If you split each of these characters off into their own zones, you'd never think they all came from the same story.
The "spell" in the story is the Marsh King's daughter's transformation between a beautiful but evil maiden and an ugly but kindhearted frog-thing. I figured I could port the general idea of being polymorphed into all the various zones. And the idea of having a bunch of different worlds where there's always somebody who's been turned into something reminded me of Super Mario Brothers 3, where all those kings have been turned into things!
So, I'd have a monarch in each zone who had been transformed, or "hexed." (It's possible I was already thinking "a monarch in each zone" before I thought about Mario at all, since I did want to work in the Vampire Queen, and since Ebenezabeth Scrooge tends to run into a lot of royalty.) Since I wanted to have six zones to match the HEX theme, I looked at the worlds from SMB3 and tried to match them. Based on "The Marsh King's Daughter" and my goal of including Atë, I knew I wanted to do a Bird Zone (World 5, Sky Land), a Mummy Zone (World 2, Desert Land), a Viking Zone (World 6, Ice Land), a Marsh Zone (World 3, Water Land), and a Vampire Zone (World 8, Dark Land). As inspiration for my sixth zone I took World 7, Pipe Land, and turned it into the sewers of Trenton, New Jersey.
Anyway, the point of the game was, you'd travel between zones, you'd restore the monarchs to their original forms, and then you'd pull out an answer somehow.
Here's how I was going to execute that extraction for the theme of HEX. At the end of the game, you'd be given some very specific and inelegant instructions to write all the monarchs' transformations into a hexagonal grid, a big hexagon of hexagons, row by row, and then you'd read a circle of hexagons to find a clue that would make you realize you now had to do the same thing, filling in the big hexagon row by row, with the objects you used to reverse the transformations. Then you would read that inner circle of hexagons to reveal the answer.
To make this work, the transformations had to be very specific. The Mummy King had to become a rutabaga, and the Vampire Queen had to be a civet. The objects used to cure the monarchs were even worse. One of them was an "ensign." It was all really stupid! So, having designed this stupid puzzle, I wasn't inclined to work on it really fast. I suppose in retrospect I was "letting it percolate."
When I found out the prompt for the 18th was SPELL, I was initially a bit ticked off, because, isn't that the same thing as HEX? But then I realized I was being thrown a lifeline! I could keep all the cool parts of my idea and come up with a new puzzle mechanic. I had wanted to do something with the Warp Whistle from SMB3, but Ebenezabeth doesn't need any help warping around. So instead why not use it to spell things!
The answers for the SPELL version were originally EGG, EDDA, DEAD, BADGE, FACADE, CABBAGE, and finally FABACEAE(!!!!). I had my wife test this out and it appeared to be too hard. That probably sounds really stupidly obvious to you, who have played the game already, but I didn't know in advance! THAT'S WHAT TESTING IS FOR. She did guess CABBAGE right away, and found that very amusing. So I retuned the difficulty to make CABBAGE the final boss. (Fortunately I hadn't designed a future metapuzzle that required FABACEAE as a feeder.)
Anyway I hope you had fun!