Over on the IRC, much discussion has already occurred about the various abilities CAP 5 could potentially have. I'll highlight some pros and cons of a few different abilities.
What we should consider:
Adaptability - SO much conversation has occurred about this ability. The ability boosts its Grass and Dark attacks tremendously, effectively making it an even better pivot for a sun team, which inherently would have a weakness to Water attacks and the Latis. As the idea is for a pivot which functions well on a sun team, this seems like one of the best abilities for CAP 5. It not only restricts its power to the specific Pokémon which it seeks to be a pivot against, it also gives it enough power to truly threaten those Pokémon, which will often elicit switches. Doubled base power will literally allow CAP 5 to wreck those types its STABs are super effective against, namely Water, Rock, Ground, Psychic, and Ghost, three of which are supposed to be threatened by CAP 5 and none of which are supposed to threaten it. However, as nyttyn will argue, it has the downside of "limiting" CAP 5 to just its STABs, as all other moves would be weaker, most of the time even when the opponent resists the STABs. Likewise, it will limit the rest of the creative process to creating it around those two types. Some believe that it will render coverage moves unnecessary; some think it will simply function as a better pivot and counter to the Pokémon which it is meant to be a threat to. Adaptability is definitely an ability that needs more looking into.
Cloud Nine - An ability which got some mentions in our conversations, but not much. It seems like it could be useful, as it temporarily ruins the momentum of a weather team. Making Hurricane and Thunder have 70% accuracy, lowering the power of the already not very effective water attacks by 33%, and making HP Fire just as powerful as normal all make Cloud Nine a useful ability. Furthermore, since it doesn't permanently remove weather, it can switch in on a sun team and remove the boost to Fire sun gives the opponents which would wreck CAP 5. It's a great ability, and would be very useful against rain teams or on sun teams in general, if only for the temporary weather removal. Unfortunately, it can help a rain team just as much as it could hurt it, except for the loss of rain to protect it from its Fire weakness. Regardless, it wouldn't be a bad option, and should not be overlooked.
Harvest - A lot has been said about this ability already in this thread, so I won't go into details about it. It makes it very versatile on a sun team, but does nothing to prevent use on a rain team. Harvest is definitely a popular option, but the real question is whether or not it would really help CAP 5 accomplish its goals. It seems to me personally that it would make it into a wall rather than a pivot.
Natural Cure or Regenerator - These two abilities both are perfect abilities for a pivot: Natural Cure allows it to pivot more reliably, while Regenerator allows it to pivot more times per battle. While a Burn from Scald, which is commonly found on rain teams, could put a pivot out of commission for the rest of the battle, and Sleep and Freeze from Spore or Ice Beam could instantly lose you a Pokémon, Natural Cure would free up your Pokémon the instant it leaves the battlefield. It would allow the Pokémon to reliably keep coming back, free from status ailments every time. On the other hand, Regenerator would keep CAP 5 healthy enough to reliably come in and out many times, even with Stealth Rocks or Spikes on the field. Neither ability would allow the pivot to deal with Toxic Spikes, but both the ability to either stay free from status ailments from any other source and the ability to heal 1/3 of its health on the switch out are great options for a pivot such as this. The big question comes down to which would be a better option, and whether or not Regenerator would be overpowered. Furthermore, neither truly limits its use on rain teams, which makes them less useful for CAP 5 specifically. If used, we would have to be careful on how we implemented them.
Storm Drain or Water Absorb - These two abilities should be fairly straightforward: on a Fire team, Water moves are common threats, and either of these abilities would limit that threat if used well. Switching CAP 5 in with either of these abilities would allow another layer of comfort for a Fire team which also threatens those Pokémon which use Water attacks. Unfortunately, Storm Drain's Special Attack boost would not be very useful for most Dark attacks, and from what others have said, it is more likely to be a physical attacker. Water Absorb seems like a better choice given what we have decided thus far. However, the question is whether it really needs a Water immunity and how that could help it on a sun team without making it useful on a rain team.
Thick Fat, or the ability which would make Yilx kill himself - This ability is much like Adaptability in use: Adaptability boosts two attacks, Thick Fat boosts two defenses. As CAP 5 has 6 weaknesses, two of which are common attacks, and one of which is extremely common on Water types, having a bolstered defense against Ice attacks would greatly benefit CAP 5. Currently in the OU meta, 68% of Politoeds run Ice Beam, which is more consistently run than any single Water move. Likewise, 69% of Starmies run Ice Beam, which is, again, more than any single Water move. (Each does have three different Water attacks which, if you add their percentages, add to more than their Ice Beam percentage, even adding to over 100% in Politoed's case.) From these statistics, it is plainly obvious that a Grass type that is meant to counter Water types is going to have trouble doing that without a resistance to Ice attacks as well. Thick Fat would not only provide that resistance to Ice attacks, it would also give a defense to Fire attacks, which would negate their weakness in rain while only lessening the weakness in sun (and making it neutral without weather). It would be a great ability, if only to get rid of the Ice weakness and to remove 1/3 of its plentiful weaknesses. It would make it that much more of a threat to any Water Pokémon faster than it, while not making it overpowered and not giving it extra use on a rain team where half of the team resists Ice and Fire, not even counting in rain's hinderance to the power of Fire attacks. Thick Fat would be a great ability, but unfortunately it would also screw over literally 90% of the artists who have submitted artwork, as almost all of them are plant-based. It should definitely be considered, though.
EDIT: Lawl, just noticed that noproblem23 included the exact same stats and reasoning for a large portion of what I said about Thick Fat. Oh well. Redundancy shows how useful it would be.
What we should NOT consider:
Chlorophyll - Chlorophyll simply would make CAP 5 another speedy Grass Pokémon which is capable of sweeping teams with Choice Specs or Choice Band and powerful STABs or coverage moves. We don't need more of those. Even if it was incapable of sweeping, being fast effectively eliminates the idea of it being a pivot and makes it more a revenge killer. That goes against the entire idea of CAP 5.
Leaf Guard - Leaf Guard serves the same purpose of Natural Cure or Harvest, largely, except that it requires sun, whereas Natural Cure only requires a switch out and Harvest only requires the berry to be reacquired. While it would not use your item, unlike Harvest, it is less viable than Natural Cure and would force you to use it only while you have sun up. If a rain team switched the weather on you, it would be just another normal Grass Pokémon, effectively. This would make CAP 5 rely heavily on sun, and prevent it from countering rain teams without sun being the dominant weather.
Solar Power - Solar Power would be a horrible idea. CAP 5 is a pivot, not a sweeper, not a revenge killer, not a wallbreaker. We don't need another powerhouse; most Fire Pokémon are already very powerful under the sun.
Flower Gift - Just like Solar Power, this would turn CAP 5 into something it is not intended to be. As in single battles it only affects itself, this would basically be a Solar Power for Attack and Special Defense instead of Special Attack, but with no drawbacks. It isn't a bad idea, but since most good Dark attacks are physically based, and Grass has a lot of power physical attacks, this would potentially do the same thing as Solar Power, but for physical attacks. Which, again, goes against the entire idea of CAP 5.
Anyways, those are my opinions and thoughts about each of the abilities discussed here or on IRC or that I have thought about.
