First of all, two closely-connected thoughts. This concept is worded in such a way that it will not be immediately evident in every single battle featuring this CAP. That is really important, because it is (almost) unprecedented. Except for Arghonaut's Decentralizer, no other CAP concept has been like that. Tomohawk grabbed momentum in every single battle it was featured in. Colossoil actively discouraged the secondary in every single battle he was used in. This concept doesn't work that way. That is a really, really big deal. Where you will see the impact of this concept is over five battles, ten battles, twenty battles. It's not about one battle, it's about usage. So when we talk about the metagame, we need to talk about more than "viability". I liked Yllnath's post quite a bit (read it right now if you haven't already) because he really emphasized how usage is competitive, how it's all about getting the best chance to win. If a Pokemon is "viable", it can be used in OU without being a complete liability. However, usage is a zero-sum game. We talk in percentages, slices of the pie. A Pokemon or a type may become individually usable, but this does not mean a real percentage change if the change drives up the usage of the prominent Pokemon or types. Countering a type doesn't necessarily drive its usage down at all, it may even drive it's usage up. Why? That's brings us to our second point. OU team building is different in BW than it was in DPP, or in BW UU, or any other metagame, excepting perhaps VGC and Smogon Doubles. The BW OU team building process is very greatly defined by team tropes. I know that we could probably distinguish between more tropes than these (like Rain stall vs Rain offense), but for simplicity's sake, let's say there are eight basic tropes: Sand, Rain, Sun, Hail, dedicated anti-Weather, Dragonspam, true heavy offense, and Baton Pass chains. The most dangerous match-ups for a team of a particular trope are basically the same no matter which one is actually used: generally there is one particular trope that gives your trope considerable problems, for which you need to have specific Pokemon that perform well against that trope. As an example, using Celebi on a Sand team. However, almost as large a threat are teams of the same trope. For a Baton Pass team, the trope is so rare that the threat of facing an opposing BP chain is negligible. However, for a popular and powerful trope like Sand or Rain, facing a same-troped theme is guaranteed. All of this to say, having Pokemon that fit on a troped team that perform very well against other Pokemon of the same trope is a massive premium, and boosts rather than hinders that trope considerably. No one wants to use a Sun team that is helpless against enemy Heatran and Volcarona. Inanimate Blob brought up Gastrodon and Toxicroak as two good examples of Pokemon that do well against Water types (and are actually dangerous against Rain teams). This is an ideal example of what I am talking about, since both of those Pokemon are used almost entirely on Rain teams, specifically to help those Rain teams beat other Rain teams. Boosting Rain will always boost Water usage, no matter how well a Pokemon counters Waters. A lot of discussion in this thread has gone into how to make underused types more "viable". I believe this is misguided. Suppose we created the perfect Rapid Spinner. It made Stealth Rock so difficult to keep down that it could be almost completely ignored as a factor. This would theoretically make Fire types much, much more "viable". And it probably would. But it would also make Dragonite, Thundurus-t, Salamence and Kyurem-b many times more powerful with it. Usage is a zero-sum game, so if you want an underused type to gain usage, you have to make sure that the change you are using to do it does not boost the dominant type in the process. If you want to decrease the usage of Water types, CAP5 has to do more than be anti-Water, or even anti-Rain. It has to be significantly more advantageous to use outside of Rain than on Rain, or risk doing the exact opposite of what the concept is intended to do. So think big picture. Don't worry so much about what CAP5 does in one game. Worry about what the metagame looks like over the course of five, ten, twenty. That is what a usage-based concept is all about.