I was really worried about this one. I think it worked out well, but only because I got lucky and solvers were inventive.
A challenge stapling together unrelated challenges is a bad idea. Even worse is if those sub-challenges are intentionally generic and overdone. The spec needs to be long and complicated to include both the "frame challenge" and the sub-challenges with their technicalities.
Gosh, I didn't even Sandbox it. What a disaster waiting to happen. Sure, the concept is cute, but would solvers enjoy it? Would anyone even answer?
I had thought of a question like this for a while. My original motivation was to parody a common strain of overdone challenges that used to plague the site. I considered making such a question as a mostly-joking dupe target for them. Perhaps by the time I posted it, many users who weren't around then didn't get the "reference", which suggests I should have posted this challenge years ago when I first thought of the idea.
I tried to get across the satirical humor in the challenge but I was worried that my initial attempts seemed too mean, and that someone could interpret it as making fun of their challenge in particular, so I backed off. Still, I feel like I missed an opportunity to lean into the absurdity. Like, if the main appeal of a challenge is that the idea is witty, that humor better actually come across. It's unusual for me to write a thematic challenge like this, so I don't have a good sense on how much to lean on theme for them.
Despite my worries, the challenge got a good number of answers with lots of interesting golfing and optimizations.
I found it impressive how answerers managed to reuse code for computing Fibonacci number/triangular number/multiple of 3 (B). I didn't see that coming for the most part. and in retrospect I got really lucky with the three sequences I chose kind-of arbitrarily. Kudos to solvers for finding some pretty parallel ways to generate the sequences and digit checks, and optimizing those that a bunch. Because of that, answers didn't feel like solutions to separate sub-challenges pasted together.
I'm glad that I resisted the urge to include primes for being so classic. I also originally had more and harder sub-challenge parts, including variable bases, and thankfully I cut down on those.
I tried really hard to write a clear spec given how weird and long it was, and I think I succeeded there. I thought a lot on how to present the different options before coming up with the fill-in-the-blank presentation, which then inspired the Mad Libs title. Still, I wonder if Sandboxing it would have led it to suggestions to make it clearer.
One helpful last-minute change was to assign letters A/B/C to each blank, which made it easier to refer to them in the details and let solvers refer to them in answers or comments. I guess a lesson is to think about clarity not just within spec itself, but for supporting answerers in writing clear explanations. Along these lines, I've found it useful when challenges name variables or concepts so that different answers can refer to them in a consistent way, which in turn makes it easier for readers to understand explanations.
Despite the challenge working out in hindsight, I think it was still probably a bad idea. Maybe it's the type of challenge that can be done once then never again. At least I definitely should have Sandboxed it.