Personally, I am leaning towards Steel.
Steel limits your opponents options, letting you predict easier, something I see as very important for this CAP.
Another good type for this would be Water. With good resistances and predictable weaknesses, It could be great for slowing the enemies Momentum.
Unfortunately these types don't have the best STABs, which may be important for turning the Momentum back against your opponent. It'll be fun to see how this turns out!
Edit: Water actually might have a nice STAB for this, just rethinking.
I'm going to back Steel. Sheer quantity of resistances forces your opponent into one of a handful of attacking types to do decent damage, allowing you to bait out offensive Pokémon of those types reliably and U-turn/Volt Switch/switch out to something which handles them well.
To make good use of a Steel-typing, of course, a secondary type with good STAB which has acceptable weaknesses/resistances would be required.
To everyone who has supported Dragon as the typing: If this CAP is going to create defensive momentum, how is this going to be any different from a bulky Garchomp or Mence? And by that I mean a Pokemon that is almost always better suited in their offensive role.
I get it. Dragon has great resistances. However, it actually suffers in STAB moves that are good for a momentum creator. Outrage and Draco Meteor are not good moves to use on a Pokemon that is supposed to create momentum. Dragon Tail going second is hardly going to help. That leaves Dragon Claw, which, while not awful, is not going to be doing a ton if the CAP doesn't have great attack. And if it did have great attack, it would simply run outrage (which we can't let happen, since the goal is momentum not sweeping).
tl;dr - If dragon is chosen, then you are committing to giving this CAP poor offensive stats, making its great STAB irrelevant.
Am I polljumping when I say we could, like, not give it Outrage?
The difference this CAP may have from Garchy and Mence is that we may give it a different secondary typing, movepool, stats, ability, or...yeah. If we make a good Dragon-typed CAP, that doesn't mean it'll be a clone of other good Dragon-typed pokemon, right? It's not like Fidgit was a clone of Hippowdon, even though they were both Ground-typed defensive pokemon, or something like that.
The only way we can make this Dragon any good at the concept is if we made it an even better offensive powerhouse than the other Dragons, or else they'll just roll right over it. Defensive Dragons just cannot be good in a metagame where other Dragons will roll right over it unless they had some kind of unique perk that made Dragon attacks do way less than they should. Give it Multiscale and make it another Dragonite?
This concept has a much lower chance of succeeding if it can't reverse momentum against the most dominant offensive powerhouses in the metagame. Dragon really doesn't have any notable perks as far as momentum reversal goes.
I support Ghost as the primary typing since it provides great opportunities to switch into Fighting-type attacks and regain momentum. Steel has been done over and over again, I really don't want to see another Metagross, Bronzong, or Nattorei emerge out of this CAP project. Although steel-types can easily switch into a lot of different attacks, it is also weak to common attacking types. Ghost's immunity to Fighting and Normal make it much more appealing in my opinion.
I've been pretty convinced that Ghost or Flying would be the best options for primary typing here. Immunities are great for this concept, and both of these types lend themselves well to secondary typings, such as Steel, Grass, and Fighting. Since we're not voting on a complete typing combination, these are really the only two I would consider for primary typing, as they lay a perfect groundwork for what we're trying to achieve. Being able to switch into common attacks, free of charge, is a phenomenal way to achieve momentum in common battle conditions. The two typings resist U-turn (important) as well as Fighting (also important), while Flying gives us an SR weakness that will open the CAP up to stronger options and greater leeway when it comes to great competitive stats and abilities later on in the process.
While this is supposed to be a primary typing discussion, this one seems to beg to be a Steel/Ghost with levitate for the best number of immunities/resistances for repeated switch-ins. In that spirit, Steel seems to be the best bet for a primary, with Ghost and Dragon okay sounding.
Obviously Ghost is my first choice for the primary typing. It has an important immunity to fighting, and is also a very adaptable typing and fits well with almost any other secondary typing. However, since this has been gone over SO MANY TIMES ANYWAY, I'm going to bring another typing down to the table.
Flying, although having great resistances is iffy for me. Rock weaknesses are the ultimate momentum breakers in this metagame, since everything and its mother carries a rock-type utility move. Also, Stealth Rock severely limiting switching doesn't help gain momentum at all either.
Poison typing is generally overlooked as both an offensive and defensive typing, but I think it could work well. The ability to instantly absorb Toxic Spikes, is the main boon to Poison-typing, however it also has some great resistances too. A resistance to Fighting, although worse than an immunity, is never a bad thing to have. Although Poison-type STAB is godawful, it isn't unusable. The Base Power of its moves are decent capping at Gunk Shot physically and Slime Wave Specially, and it hits many offensive threats neutrally. Poison-type mons are also immune to Toxic, which gives it an advantage in that it can break momentum in Stall teams that rely on Poison to deal damage. Steel-typing, although also being immune to poison, gains a Fighting type weakness in the process. Poison-typing, along with Ghost, is also a very adaptable typing, and can combine well with other typings in creating a great pallet of resistances, while contributing fewer weakness than most typings can boast.
I say Normal. It's always had the coolest pokemon (Snorlax, Blissey, Porygon-Z,Ambipom, Exploud, etc.), and has always been a decent type overall. 1 weakness and 1 immunity of the defending side, and 2 resistances, and 1 immunity on the attacking side. To mitigate the painful fighting weakness, why not make it part ghost type? Thing about it, immune to the currently unresisted combo ghost and fighting, not to mention normal moves like fake out as well. Pursuit hurts, but maybe give it Justice Heart so people will think twice before giving it a 1 att boost (it doesn't make it an immunity though). As for momentum, this pokemon will destroy the momentum of a Shandera (what is it now, Chandelure?) with Choice Scarf, Roopushin (Conkeldurrrrrrrrrr), and Revanankh in CAP. Ideally it should be pretty defensive, with a decent attack stat.
We want ideas that take into account what has been previously discussed about the Cap right. When I looked at this post one type stood out for me. (Maybe because it is one of my favorites but whatevs.)
Putting my support behind Poison. Poison has never been a good type for a sweeper. It gets super effective coverage on an extensive list of Grass, period. However in contrast to this it hits only hits Ghost, Ground, Poison, Rock and Steel for less than normal damage. One thing I notice about 4/5 of those is that they are weak to some very common attacking types. In other words poison fits the first two of these points perfectly.
Poison is weak to only two types, Ground and Psychic. While this may seem to go against the 3rd point it actually helps it. Not many Pokemon use Psychic attacks but those that do (And they are some of the top tier threats) are easy to read. Which greatly helps. The Ground weakness, while undesirable is a common attacking type that is again easy to read. The physical sweepers that Poison will be switching in to time after time aren't the ones that commonly use Earthquake. I'm speaking here of things like Fighting and Bug types. On the special side most Grass sweepers hate facing Poison types.
As for specific threats. Pokemon such as Breloom, Virizion, Conkeldurr, Volcarona, Escavalier, Whimsicott and sun sweepers are all relitively common Pokemon that will have big trouble getting past a Poison typed momentum Pokemon.
In addition to these points. Poison helps against stall if we keep it grounded. It also isn't weak to any hazards.
So basically I am thinking of a type that forces both Defensive and Offensive switches. I have one main type in mind when it comes to choosing which.
First on my list is Dark. It has a decent coverage when paired with another suitable type, hits Super Effective damage on Ghost and Psychic types, both of which are really popular in today's metagame. On the defensive side, it has an immunity to Psychic type attacks and resists Ghost type attacks. It does however possess a common weakness; Fighting as well as Bug. Another reason for Dark typing is that it IF it was to have the move Pursuit, it would deal heavier damage IF it had the Attack stat to go with it.
As well as that, Psychic and Ghost would also make some nice options.
I support Ghost too. Anti-Spinning is really amazing and fills perfectly in the concept. This type allow outpredicting (against Ttar) and in this metagame where Fighting-Pokemons are everywhere, having a Ghost-type is the best way to gain momentum.
Flying can be nice too. It's an underused type due to the lack of good Pokemon / attacks, but it can be interesting to see how a Flying Pokemon not-named Gliscor can change the metagame.
If I had to choose one typing, it would have to be a Dragon. They can come in on a lot of stuff thanks to their great resistances to Fire, Water, Grass and Electric and steal momentum by forcing out the opposition with a STAB Draco Meteor or another high powered move. This pokémon would also have to be given no boosting moves, or else it may become a powerful sweeper that would ruin the concept. Also, we must be wary not to make another Flygon, as suggested by Chou Toshio, although levitate would greatly benefit this new CAP in that it could switch in and out of Spikes and Earthquakes with ease. I feel that a great secondary typing would be Ghost, as this would grant immunities to Psychic, whilst also being able spin block. Rising_Dusk explains why Ghost would be such a good choice for this situation.
After a great deal of discussion in #cap, I'm reaffirming my preferences.
Resistances are important, but the level of offensive prowess in Gen V is so great that even resistances can be overcome. Someone mentioned Landorus punching through even an Impish Breloom with Earthquake. Now Breloom isn't the most defensive mon out there, but crashing through resistance and a defense boosting nature is no laughing matter. Some of the sweepers are just too absurd. Last Gen this applied primarily to Dragons, but now they aren't the only threats with dominating force. Ultimately the gold standard for switchin damage is zero, and Ghost gets that gold standard on two attack types. One is Fighting, one of the most ubiquitous attack types, and the other is Normal, home of Rapid Spin. Normal attacks aren't totally limited to Rapid Spin though, as Excadrill and Gilscor have been putting moves like Return and Facade on their movesets to supplement the huge power they have behind Earthquake.
If that weren't enough, Ghost also adds a resistance to Bug to its benefits, which allows it to come in on U-turns and resist them, minimizing their impact. Since U-turn is often used by opponents to maintain momentum, and often weak ones at that, the less damage a Pokemon suffers in the exchange the more adequately it can respond to the new threat. The Poison resistance is largely irrelevant, as any Poison attack outside Toxic or Clear Smog is unlikely to be seen, and neither of those is used for direct damaging purposes.
Though its immunities are one fewer in number than Ghost, the one immunity it possesses is extremely important. Ground immunity spares it from not only Ground-type attacks, but also Spikes and Toxic Spikes damage. With Ferrothorn and Accelgor providing brand new Spiking options in addition to the new relevance of Cloyster, Spikes is the new hazard threat to watch out for. Stealth Rock weakness is still undesirable, but not to the extent it was in DPP. Additionally Flying carries with it a resistance to Fighting and Grass attacks and derives the same benefits as Ghost when it comes to switching into U-turns.
Flying's final quality comes in its relationship with Roost, which allows a Flying-type Pokemon to restore 50% of their health while evading extra damage from the common attack types they lure in, all for the low cost of a temporary vulnerability to Ground-type attacks and a removal of their other resistances. This relationship helps a great deal in supporting the imperviousness trait I brought up in the concept assessment thread; it allows our Pokemon to keep itself healthy enough to absorb more attacks. Moves are of course not decided yet, but this is a unique trait to keep in mind for later polls, as it comes in quite handy for countering certain Pokemon.
Both of these would make excellent primary types for our first CAP Pokemon in the 5th Generation, and can blend in well with other types to achieve project objectives.
I agree with Deck, Ghost and Flying seem to be our best options here. It just depends on what we want to get out of this CAP. Ghost helps Stall by spinblocking, while Flying screws Stall over by being immune to 2/3 of the entry hazards. But if I had to choose, I would pick Ghost because Flying always seems to be a secondary type. You never see any Flying/Normal types do you?
To have a pokemon based around momentum, it has to be able to stop the momentum of commonly used pokemon.
Arguably, the most common attacking types in OU as of now are Dragon, Fighting, Ground and Water. All of which have rather powerful STABS, or, in Water's case, have Double STAB due to the weather.
Obviously, no single type resists all of these. In fact, no duel type can resist all of these types [Only Steel Resists Dragon, and it's weak to Fighting. Going Steel/Ghost will leave us weak to Water, even with Levitate]
In addittion, I feel that if we go, as many people are suggesting, with Steel, we will just end up with Nattorei/Scizor. Let's face it people, when it comes to steel types and momentum, Nattorei and Scizor have it covered.
Nattorei can come in on anything that's not fighting or Fire, and threaten with 120 BP STABs off of a more-than acceptable attack stat. That screams momentum to me. Sure, he cannot U-Turn or anything, but he does what the Steel-type does best, stopping mometum. When it comes to gaining mometum, Scizor has Steels covered in that department, with his typing, bulk, threatening Bullet Punches, and U-Turn.
Personally, I feel we should go with the Flying type.
Why is this?
#1: The Flying ype provides an immunity to Ground, resistance to Fighting, and neutrality to Water and Dragon.
#2: The Flying type has some decent moves now, and generally is wide open in terms of movepool. Tailwind and U-Turn are also good moves to swing mometum.
#3: One of the biggest throwns in the Flying type's side, Stealth Rock, is used a lot less this generation. Between the loss of Spinblocking in Rotom-A, Mischevious Heart, Team Preveiw, and Magic Mirror, as well as things that you can't give that free turn to set up SR on, such as Blaziken or Renkulus, SR is no longer what I would consider a Standard Battleing condition [Indeed, I see more Spikes than SR... probobly due to the fact that they hit Nattorei harder]
I believe the two best options for CaP1's primary typing are
Ghost: Immunity to Fighting is a HUGE plus in Gen V. While there are some defensive ghosts, Evo Stone Dusclops, I think it would be very cool to develop CaP1 as the primary defensive ghost pokemon. In Gen V we lost the premier spinblocker, Rotom-A and losing all your hazards to a Rapid Spinner is (I think) the single biggest lose of momentum most teams can face. Ps, having the opponent crash on their Hi Jump Kick is AWESOME!!!
Steel: A plethora of resistances, when I think of defensive pivot pokemon usually steels come to mind, Heatran, Ferrothorn, Jirachi, Bronzong
It seems like we have reached something of a consensus, and the best options would appear to be Flying, Grass, Ghost and Steel. These possess multiple useful resistances and immunities, and generally enough of an offensive base to not be utter set-up bait.