Sub-grid will be changed in the next version to 'thickly outlined square regions within the grid'. So in the example there is one. Hope it is clear now.

The Puzzle Fusion concept looks nice. However, I think a little more precision is needed in the rules for Spiral Galaxy^2.

Does the combined region have to be continuous i.e. made up of edge-connected cells? I assume yes. Does the symmetry exhibited by the combined region have to be 180 degree symmetry. I assume yes. There is at least one alternative solution which has a continuous region exhibiting mirror symmetry.

I'm curious: Who made the Skyscrapers² puzzles and (who) had the idea for it? If you do not want to tell the name(s) before the championship, that's of course totally fine.
I'm asking because I had the same idea some years ago leading to this two puzzles:

https://logic-masters.de/Raetselportal/Raetsel/zeigen.php?chlang=de&...
https://logic-masters.de/Raetselportal/Raetsel/zeigen.php?chlang=en&...

Anyway, you have here two puzzles for training (with the small example even three). And I really like your much more elegant name than the one I've chosen :-).

just a graphic issue. in ARAF^2 one of the areas is of the wrong shade

Its not a graphic issue, unless I am misunderstanding this. Consider the solution as each region containing four circles, and the shading within each region is just to show the further division into regions containing two circles (i.e., regular Araf). The order of the shading is random, its just to depict differentiation.

Please bring this up again after the WPC and we can discuss it ;)

The area on the right has only 2 circles, the area next to it has 6. At least this is what my printer prints. The area containing clues 2 and 6 should be of the same colour of the area containing 12 and 3

You're looking at it wrong. The first division is the black lines, giving 3 areas with four circles. Then, within each black-bordered area there is a light and dark area, both with two circles. The shaded areas are not connected. They just differentiate between the two areas within a single black-bordered region.

I understand this. If you read back, my initial statement was referring to just a graphic issue. I see the think lines, I just say that choosing the same grey shade for the two areas on the opposite sides of the think line is misleading.

Ah ok. I don't think we will be changing this since in our IB prints the thick lines come clearly. Thanks for the note though, we will clarify the same at the Q&A.

Forgot to reply to this, but had noticed it and made amendments to the rules that are there in the current IB version available.

I come back now to my questions from #23617. Can I please have some information/thoughts from the author(s)?

Ok, so its time to answer this. I was the one who came up with the Skyscrapers² idea. It was actually first meant to be a Sudoku variant in the Innovatives round of the WSC, then I believe we had the thought of moving it to some of the other rounds before I had ever written a Sudoku. Eventually this was all scrapped and we went with a puzzle at the WPC. After that, I wrote the Windows [Windows] puzzle, and it was actually these two that gave us inspiration for a full round, after which Rohan thought of Spiral Galaxy², I thought of Araf² and Deb thought of Palindrome². We had some other ideas too but they were rejected for being too complex or not fitting the theme, and eventually because the others fit so well as the concept behind the puzzle getting repeated, even the Windows variant got removed even though it was one of the first ideas, and it eventually got moved to Round 4, as WPC participants will know.

You definitely came up with the idea before I did though, by about 3 years :) I wasn't aware of it but maybe that worked out well because thinking of it as an innovative variant organically lead to an entire round. I'd like to see if there are more ideas along these lines which fit the concept.

Yes, that's great :-).