I'm not English native, so if you find mistakes, don't whip me. Please.
Bleh, Hustle. We really don't want to promote luck. Maybe I'm biased because I hate overhaxxed matches, but I don't understand how is it fitting to the concept.
Yes, it brings "risk" and "reward". But you can't control the risk nor the reward. Praying each time you use Megahorn doesn't promote smart strategy at all.
I support No Guard. While it obviously gives us 100% Megahorn (and Fighting coverage, probably), it also let up use a more supportive way : WoW / Hypnosis or even gimmicky options like Scary Face or Glare (Hello ScarfTerrakion !) without affecting the whole movepool. We don't need DynamicPunch or Inferno to use No Guard effectively (and it won't outclass Weak Armor).
Moreover, when bringing CAP 4 on field, it will, from its simple presence, make think twice before doing anything, from both players : you bluff just by going in : do you have a "glass-canon" set or are baiting your foe's scarfer ? But it's not only luck thanks to Team Preview. But several people have argued about No Guard better than me.
Illusion is nice too. I think there are lots of opportunities with it, but idk if they are worth it. Rebound (IIRC) is a fine choice, if it can be chosen.
Liquid Ooze, while probably not a 2nd option, is viable as a Dream World Ability.
What about Cloud Nine ? It is not the riskiest option, of course. But CAP 4 has a very interesting interaction with other weathers :
-Sandstorm : Most notably, we remove the x1.5 Sp Def bonus to Rock and make Landorus weaker. Ok, not a big deal. But all in all, SS is a bad weather to CAP 4. Whenever he comes in field, he is in danger. With Cloud Nine, we can find him some utility (forcing Terrakion out without Psyshock).
-Sun : CAP 4 resists to Grass but is weak to Fire, the two main types found under the sun (this, and Dugtrio). CAP 4 will bring an interesting problem : will we try to disrupt the momentum of Chlorophyll users, at the risk of facing Heatran / Ninetales ? Because we are using Weak Armor, CAP 4 will probably outspeed most Chlorophill (and most notably, Venusaur). It is not just prediction. I think.
-Rain : The obvious thing is that CAP 4 will take normal damages from Water-moves. It means a lot. While he isn't resisting to ANY common types (and weak to Hurricane), coming into a non-Rained attack still turn the tide of the battle.
But of course, there is risks. Rain is still rain. Using CAP 4 to deal with it is just asking to Tornadus / Hurricane-users / Scizor etc... to come in. Both you and your opponent have to change your play-style. Both of you must take risks : you can neuter SOME strength of its attacks, but he still have a lot of tricks under his belt.
And of course, it does nothing to weatherless battle.
That's why I'm not fiercely advocating it, because it is, by far, not the riskiest option we have (and it does nothing without weather). But when playing against / with (hey, I've heard you use Kingdra to counter my rain ?) weather, it forces both players to change their mind. The weather-player can't just use weather-boosted options (Starmie without Rain is significantly weaker) but the CAP 4 user can't use it to check everything.