Couple of things. Firstly, when looking at what threatens this CAP, we ideally want to make sure its "hard walls' (thanks to the less than stellar offensive typing we picked, you can bet there will be a few) are not common pokemon. This is due for several reasons. Currently, when looking at the OU metagame, there are several pokemon that are "common", in that they are seen on many teams. If we made CAP 6 (hypothetically speaking), weak to Scizor, CAP 6 wouldn't be used, simply because Scizor is a good pokemon in of itself, and it would get used both for checking CAP 6, as well as doing everything else it does well. Due to the high risk / high reward playstyle of belly drum, we do not want to make it easy to hard wall this CAP, in order for the belly drum to be rewarding. For instance, Magnezone is by no means a bad pokemon, but it experiences less use than other OU pokemon because it offers less to the team. Jolteon is also in a similar boat. In this manner, I would prefer seeing these sorts of pokemon hard counter CAP 6 (Jolteon is a bad example because it fails at countering the thing), because it requires your opponent so make a conscious effort to use these pokemon, in having to pick a mon that might not be that "amazing" in order to hard wall the Belly Drum Power of CAP 6. This, to some extent, balances out Belly Drum, in that to fully counter it, your opponent has to use a less effective mon to shut you down, rather like how Thundurus-I encouraged people to use the uncommon Quagsire and Gastrodon, to better counter it. Despite this, CAP 6 still has to have revenge killers, and we need to nail down similar criteria. There is a large difference to this stage compared with the previous one. Firstly, your standard revenge killer on a standard OU team is a "catch all" for several common metagame threats. Its why Scarf Jirachi, Scarf Keldeo etc are common scarfers because they cover most of the more aggressive set up sweepers in the metagame. CAP 6 needs to be covered by a currently effective revenge killer, because otherwise it opens up paths to players being forced to use a weak scarfer JUST to revenge kill CAP 6, as well as a strong scarfer to revenge kill all the other threats of the meta. On the flipside, your revenge killer has to be uncommon enough, to justify using CAP 6 as a belly drummer in the first place. If everyone is running Scarf Keldeo (and a lot of people are), and CAP 6 (hypothetically) doesn't beat Scarf Keldeo, then why on earth would I bother using CAP 6 to Belly Drum (or at all), in the first place if it loses to the common scarfer(s) out there? This is the exact scenario I was worried about when we picked this concept, because it requires us to make sure CAP 6 is checkable without going to unreasonable lengths, while not making CAP 6's counters so common that it hurts the viability of using Belly Drum in the first place.