Weak Armor
An excellent choice. Real potential, risk involved in switching into hits. Potential for unwanted effects too if you haven't fully thought things through.
Hustle
This ability is clearly the epitome of risk, but is apparently not what we want as discussed previously. I can't believe somebody actually suggested this ability was too weak though. This is one of the strongest abilities in the game, but one we don't need to use. I we want CAP4 to have an enormous attack stat, we can give it an enormous attack stat. We don't need to make it miss all the time.
Trace
I like this one. It involves switching CAP4 into the right pokemon, which can at times be difficult. I do feel like the reward is a little lacking here though. The majority of abilities in OU are of relatively little use to CAP4.
No Guard
By a country mile, the worst option that has been suggested so far (edit: except for tinted lens). Just because we decided that the kind of risk we wanted was not hax-related, does not mean that we have to go out of our way to remove it. We just decided that luck based risk was not the concept, not that it had to be removed at all cost. There can be absolutely no denying that this ability removes risk, and does nothing but remove risk. This ability might have a drawback, but not an especially significant one, nor one that you can particularly control. A drawback does not make an ability risky automatically. In this case, it makes it less risky, because a risk for the opponent is a risk for you. I'm going to say this again: a drawback does not entail a risk. A drawback merely makes a pokemon worse unless you have some control over it.
Quick Feet, Flare Boost, Toxic Boost, Guts etc.
Bearing in mind out CAPs vulnerability to residual damage, I think the running of a status absorb would be suicide. I would be highly surprised if many people used one. I might even go as far as to say that deliberately switching in to a status move would be suicide. As such, these abilities merely provide insurance against status – they could almost be seen as safe. Might have been good with a different typing, but on balance, I'd rather not.
Synchronize
Again, I just think this is a "safe" ability really. You're not going to deliberately switch into status moves generally, so it's just insurance.
Download
I think this ability would only really qualify as risky if CAP4 were only to have one good attacking stat. Otherwise, this ability might carry relatively little risk. Look at Genesect – because it commonly runs both physical and special moves, which DL boost you get is often inconsequential. Also, many pokemon have balanced defensive stats, and would therefore merely leave you guessing as to which boost you'll receive (pure luck) rather than just relying on you getting Genesect in on the right pokemon. Still, a decent choice.
Regenerator
This ability is strong, all of the time. It attempts to cancel what we deliberately did when we determined CAP4's typing, making it weak to residual damage. A very safe ability, and a poor choice.
Unburden
Yeah I like this one. One time use (in all likelihood) so there's definitely a risk involved there.
Moxie
I actually think this one might work well. If your risk taking / good play pays off and you get a kill, you have a potential for more, thereby accentuating the effect of the risk. Only worry is that we didn't want CAP4 to have any real counters, and moxie makes checking stuff by sacrificing things rather tricky.
Rattled
This one is pretty cool. Requires you to take an enormous risk, allowing a super effective move to hit CAP4, and provides a reasonable reward in the form of a speed boost. Could produce some interesting mind games against Pursuit users. However, I feel that the reward might be too small to justify taking a super effective attack.
Swarm
A rather boring ability, and difficult to take advantage of deliberately bearing in mind Cap4's residual damage weakness. Reward is not great enough to justify deliberate lowering of health.
Speed boost
No idea why this was suggested really. This is not a risky ability, but a consistent and very strong ability.
Simple
Stat-up moves are definitely somewhat risky so I suppose this could work. It doesn't really fit all that well into the "no counters, plenty of checks" thing very well though.
Sheer Force
I don't get it. Removes luck-related things and life orb recoil, both of which would have been appreciated for the concept. If we want CAP4 to be powerful we can make it powerful.
Technician
Don't get it either. It's easy to use, and continuously in effect.
Tinted Lens
Extremely safe ability. Tinted lens is really easy to make use of, is absurdly strong, and goes against what we've said in previous threads – that this pokemon's STABs shouldn't be spammable. The second worst of the lot. edit: nah it's actually the worst lol.