[capefeather]

One thing that I think isn't being touched on very much is viability. We've mentioned a lot of moves and abilities carried by Pokémon that simply aren't viable, and a natural question that comes out of this is, "Why?" Why is it that some risky tactics work and others fall flat in OU? Is it due to the tactics themselves or is it due to their availability to existing Pokémon? Asking ourselves this should shed some light as to whether it really is a good idea to pursue something like a Belly Drum sweeper or a "wall" with only Rest as a recovery move. Both of these are concepts that are known to be unsuccessful, and I really think it's the moves themselves that are the problem. Setup moves that don't boost Speed or one of the defenses tend to provide relatively low reward for the setup turn in general unless the user has a good priority move. Considering this, Belly Drum strikes me as being overkill without much potential reward in return.

I'm not sure I'm much of a fan of a Pokémon whose effectiveness is dependent on the team matchup. I find that the effect of such "niche Pokémon" like Gastrodon is that they are only chosen when the team really needs to have that niche on a single slot. Maybe the rest of the team struggles with offensive Water-types and rain stall, so it uses Gastrodon to absorb Scalds while having Steel-types or Poison-types to take Toxic and/or Toxic Spikes. Thus, the question here wouldn't be so much about the risk that the Pokémon poses, but instead about whether the team needs that quick plug, and how much support the Pokémon needs. This is also why I worry about the idea of weather dependence. I additionally worry about suggestions like Normalize for this reason as well.

Counter / Mirror Coat / Destiny Bond is an interesting suggestion. Wobbuffet immediately comes to mind, though as we all know, Wobbuffet is not OU. The usual thing that happens with Wobbuffet (at least against non-Choice offensive opponents) is that it has to choose between using Encore and risk being 2HKOed, and using Counter or Mirror Coat "naked" and risk whiffing. There's also the aftermath, where it is probably weakened and must face whatever it is the opponent has planned next. It makes me wonder how we could even make Counter or Mirror Coat worth using. Destiny Bond is similar, and I've seen Froslass in particular use it a lot in UU. Again, it can whiff if the opponent doesn't finish the user off, and again, it makes me wonder how we could make Destiny Bond worth using.

These are some of the roles I can see CAP 4 playing (not necessarily mutually exclusive):

Fast and powerful, but weak to priority. This would lead to risky situations between priority users like Scizor, Dragonite, Breloom and Mamoswine. More than that, though, it also places risk on the priority users! Latios versus Scizor is a decent example of this, since if it switches out it risks eating a Pursuit or the switch-in eating a U-turn, while if it stays in, it might eat a Bullet Punch and have to struggle on low HP. Conversely, Scizor has to decide whether Latios has (and will use) Hidden Power Fire to brush it off entirely, and if it goes for the Bullet Punch, it has to worry about being locked into that move against a switch that resists it and might set up on it. The decisions, then, depend on what information has been revealed and how much each player can afford to lose Latios/Scizor. This could actually be an offensive or support role, since a similar scenario could be achieved with something like fast Will-O-Wisp with priority weakness.

Slow priority user. The theme I briefly mentioned before comes into play here, as in this scenario, CAP 4 would take the role that the opponent takes in the previous scenario, and possibly vice versa. Sucker Punch has been mentioned a lot, yet it's going to have a hard time working since the user has to deal with Steel-types in addition to competition with a lot of existing slow priority users. Toxicroak is a good start, but if we're to use Sucker Punch and possibly Pursuit, we'll probably have to do better.

Rapid Spin. The idea here is to have a spinner that can't beat spinblockers if it tries to spin, but can set something up on them instead of using Rapid Spin. Forretress, for example, does not really like Jellicent at all, but it has Volt Switch, Spikes and Toxic Spikes at its disposal to punish a Jellicent switch-in. A common argument for Excadrill going to Ubers was that it could set up Swords Dance on spinblocker switch-ins and beat them.

Spinblocker. Obviously the counterpart to Rapid Spin. Blocks spinners like Forretress, Donphan and Starmie, yet if they set up something else on the switch, well...