One potential caveat to
Bulletproof Glass is that in the absence of good defensive stats, there's a good chance we'd have to rely heavily on a top-tier defensive typing and/or ability, and in that way it could be constraining. Of the example mons listed in the submission, only Crobat arguably has neither. Some other examples that come to mind are Poison Heal Breloom in past gens (acts as a defensive mon despite awful defensive stats because of an insane defensive ability), Defensive Mawile in PU pre-DLC2 (I don't know if it's viable anymore, but it was an extremely prevalent defensive mon with 50/85/55 defensive stats- it just had arguably the best defensive typing in the game as well as Intimidate), and perhaps even something like Clefable, which isn't actually that bulky, it just has a stellar ability and a good defensive typing.
I fully expect that ability discussion threads would be clogged with
Magic Guard, Magic Bounce, Poison Heal,
Regenerator, Prankster, etc. even more than they usually are, while Fairy and Steel typings would factor heavily into typing discussion. These are just by far the easiest ways to make a viable defensive mon with mediocre bulk.
I suppose it's ultimately a personal preference, but I love CAPs that explore underused abilities or traditionally mediocre typings, and this feels like it would inevitably lead to the opposite.
Edit:
StarFalcon555 Oops, sorry, I'm not up to speed. Good to know!
You got to admit though, that one thing that has been even more prevalent throughout CAPs history than CAPs with good typing, are fast bulky attackers, that have pretty optimized stat spreads and good to great abilities. So I don’t see how any other concept would really be different in what you see as something boring.
In reality I think this concept would do well in setting the result apart from almost all other CAPs.
Hidden Potential aside from being bad flavor and a frankly entirely unnecessary game element to study through CAP, runs a high risk of being overpowered. The only reason this works at all on Silvally as a non-broken Pokemon is the 1) relative predictability, 2) changing of typing of Silvally that makes using strong offensive typings like Ice have a drawback defensively, and 3) Silvally's well-rounded good but not excellent stats. In CAP world this Pokemon would most likely get a good, reliable typing, be totally unpredictable which of many strong attacks it is using, and likely have far more targeted stats to the point that it is a bona fide threat. And once the CAP has reliable typing and better stats, I strongly question whether it will genuinely use a Memory + Multi Attack vs any other item and move combinations.
This one has gotten a lot of talk about how it would bebroken and competitive.
I don’t believe it would. Actually I think this CAP will struggle to actually do anything of significance, because there is one thing immediately balancing almost all physical attackers that CAP could create, which is pur favorite Catbird

.
This CAP would need an exceedingly high physical Attack to not be blanket walled by Tomo with any physical coverage, that is not STAB. SE non STAB Multiattack would need a
fully invested positive nature 147 base attack to be able to reliably break through Tomo. Since you can’t boost Multiattack with an item, you would need to drop the coverage you could get through it and use it as a STAB.
A little lower there is another physical Wall called Toxapex that could handle anything below
126 Atk.
So if we don’t give it dedicated Special options to break past these, I fear rather than being broken it would just not become viable as a Coverage monster.
Now there are two concepts I really love to see happening.
The first one is „defective ability“ the second is „limit break“.
Both of these have a lot of interesting design space.
I don’t agree, that having only a small pool of viable abilities would be detrimental to the „defective ability“ process.
Actually I believe that these would have us think way outside the box and dissect what makes for a viable mon in unprecedented depth.
Looking into the question, if a bad ability could only be balanced by other stellar traits or if it is possible to achieve viability without going all out in the other areas is just so interesting to consider.
I also believe, that CAP 29 would turn out to be a unique mon that would be so cool to see in competitive.
„Limit breaker“ has much more depth, than most give it credit for. There are so many pretty unexplored mechanics, that would all need very different approaches.
While I think we would have to pick one early on in the process to determine how to proceed, I think each and every of them would turn out a mon that is fun to play with.