I am here to explain my stance on why
No Guard is absolutely my most preferred ability:
My first point has been touched on a lot in this thread. No Guard removes miss-based luck from both the user and the opponent. Why is this important? As people said, No Guard is especially relevant to this typing because it is weak against inaccurate moves such as Fire Blast, Stone Edge and Hurricane, while being neutral to the potentially rain-boosted Hydro Pump. No Guard was, in fact, one of the first abilities that came to mind as soon as people started talking about being weak against Stealth Rock in the typing stage. On the user's side, No Guard broadens the options that we can put on CAP 4, with moves like Focus Blast (I always feel a bit uneasy whenever we put Aura Sphere on a CAP) and Thunder, as well as status moves. Megahorn and even Zen Headbutt also benefit from No Guard.
But that's largely been covered already. How is all this relevant to risk versus reward? The basic answer is that the choice pairing that both players make resolves in the way that it's "supposed" to; the RNG doesn't get to decide that rock beats paper for this round. Both players have to own up to the consequences of their decisions. This is actually very important because
luck impacts the decisions of players and this impact is often not conducive to decision-dependent consequences. Consider the scenario in which someone is trying to stop a Reuniclus sweep by compelling it to keep using Focus Blast (say, by switching in a Steel-type). If Focus Blast hits (and the target is KOed), the opponent failed on what we'll assume for the sake of argument was its best move. If Focus Blast misses, the Reuniclus failed on its best move. So the resolution is either that the target is punished at a rate of
70%, or that the user is punished at a rate of 30%. It's not just about whether a move is more likely than not to hit because punishment for making the best move goes both ways.
The luck factors in Pokémon compel behaviour that is perverse in the sense of maximizing the importance of skill over the importance of luck. Often, the optimal decisions
increase the effects of the RNG for the sake of increasing one's chances of winning. We can argue all we want about how much luck there is in a single rock-paper-scissors / poker / prisoner's dilemma scenario. At least said "luck" depends entirely on the players and not on an outside factor like the RNG.
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I'm also going to go ahead and name some suggested abilities I like, both of which I didn't like at first but warmed up to after some thought.
Weak Armor sounds on its face like a pretty gimmicky ability that maybe "works" once in a battle against someone unsuspecting. Yet, it could actually bring an interesting dynamic, as supporters have said. It's a way to give CAP 4 a good switch-in to physical attacks and great Speed, while simultaneously weakening it against priority moves (all of the relevant ones are physical) and faster physical moves. The player has to decide on how CAP 4's matchups are altered after switching into a physical attack. I also kind of like
Analytic, even if CAP 4 doesn't turn out to be all that slow, particularly because
it works on opponent switches. A power boost by Analytic could be counterbalanced by lower offensive stats, so that CAP 4 can land 2HKOs and OHKOs on switches, but if the opponent stays in, CAP 4's offense is significantly weaker. All that said, I'm not sure of what people who want a setup sweeping set out of CAP 4 would think about Analytic now that I've brought this up.
The thing I personally don't like about Unburden is exactly that it's kind of a one-shot thing. Yet, I know that this is just my preference, and people are free to disagree. A similar sentiment goes for Illusion, since it breaks as soon as the user is hit. On the subject of status boosters, well, I'm not sure of what I think of them. Guts / Toxic Boost / Flare Boost in particular are pretty much "extreme Life Orb", which I can see being argued either way.
I think that's everything I wanted to cover...