On the screen where you need to press the middle button 3 times, you also have to press the first and last button once because there is no other way to press the one in the middle without pressing the first and last as well
The way I did it was run to the middle button, strafe back and forth to activate it 3 times, float down to the left, and then straddle the cliff edge by the first button (which I activated once on the initial run) until it was back to the circle symbol.
So it went like
0 0 0
1 1 0
1 2 0
1 3 0
and kept activating the first until
0 3 0
A player wouldn't need to carefully straddle the cliff to keep activating the first button either if that is too difficult, as one could activate the first button once, fall down to the left, and repeat until the first button is back to the circle symbol.
I don't think it's intuitive enough that the solution is 1 3 1, since the player could also run back to the start to make it 2 3 0. It's such a minor thing though and I could have figured it out with more trial an error so it doesn't matter
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As for the drawbridge thing, I did that run 99.9% without cheats (only teleported on one screen with the puzzle described above ^). It didn't happen on 2 of my other save files, fwiw (including the first with gratuitous cheats) so who knows.
No big deal since I can go to a different save file.
The coin refund thing is a good idea, but not possible afaik in KS+.
I don't know about level creation, is there a way to have the powerup itself freely respawn once "destroyed"? Alternatively could have one of those roman numeral gates, but I'm assuming they're tied to the golden creatures.
I'll give the code sections another go and look out for hints in the surrounding areas! Thanks for such a great level.