- What types exemplify Pokémon that provide strong offensive pressure for a team? What are these types specifically targeting that make them desirable for this purpose? What about these types makes them great spammable options?
I believe the best most efficient ways to provide strong offensive pressure are either,
a type that has a good matchup against many prominent important threats in the metagame, or one that very few common Pokemon can easily switch into.
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Ice-type probably fits this criteria the best, as it targets Dragapult, Hydreigon, Mandibuzz, Jumbao, and Kommo-o and its neutral coverage is also great considering most resists like Aegislash and Rotom-H can be worn down with relative ease.
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Ghost-type doesn't really target any particular threats, as Dragapult and Aegislash can still hit back with their own super-effective STAB but is only resisted by Hydreigon, Mandibuzz and Colossoil, making it a very spammable type in the current metagame.
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Fire-type is probably the second best Type at targeting prominent threats, as it scares Corviknight, Aegislash, Jumbao, Excadrill, and Ferrothorn; although its also relatively easier to check by things like Dragapult and Hydreigon.
-Other good types to take into account are
Fighting, Rock, Fairy, Electric, Normal, Flying, and Ground. These are probably not as powerful as the above choices, but this is not necessarily a bad thing, as they are still good offensive types, and with less power the risk of CAP 27 turning into a generic breaker/sweeper is significantly lowered.
- What types typify Pokémon that can supply ample team support? What is it about these types that provides adequate defensive durability in order to preform repeated utility? What are some key resistances we should consider for optimizing durability and switch-in opportunities?
As Pipotchi mentioned, types with attacking moves that also have innate utility would be very useful, as moveslot economy is going to be an important factor in how much utility we can fit in our sets, for this reason
Dark (Knock Off),
Water (Scald),
Bug (U-turn),
Electric (Volt Switch, Discharge),
Fire (Lava Plume), and
Normal (Body Slam) are naturally good options. I'd say that on this list Normal and Bug are a step below the others, as they don't provide as many valuable resistances, but they're still decent.
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Steel is always going to come up if you want to discuss defensive types, and for a good reason, as it provides more resistances than any other type, something that is always important to maximize your chances to switch in. That being said, I feel like in this meta this type this is probably not as good as it used to be, as some of the most prevalent threats have neutral STABs like Dragapult or have coverage to bypass it, like Clefable and Syclant. It still definitely should be considered, but I wouldn't call it a main contender.
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Water is another generically good defensive type, an Ice- and Fire-type resistance could be great valuable assets, and a STAB-boosted Scald is a great way to spread status, at least if we can find a workaround the omnipresent Water-type immunities.
- Where do the types that fall under the categories of offensive pressure and durability overlap? What specifically do these types offer that make them desirable for both categories given the landscape of our meta? Since we are trying to establish a balance between offense and durability, do any of these types facilitate team success without risking becoming too offensively or defensively potent?
-Fire-type is a really good all-rounder, it has really good matchup against many significant threats both offensively and defensively without being too overwhelming, and also has access to good status spreading STAB moves, making it one of the most attractive options in my eyes.
-Electric-type is another solid pick, there might be more Pokemon resistant to this type, but it still has decent enough coverage in the current meta and Paralysis can be a very powerful status to spread.
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Dark-type gives us access to STAB Knock Off, and while it doesn't offer much defensively, a Ghost- and Dark-type resistances can be very useful. My fear with this type is that a strong and spammable Knock Off might be too powerful for our own good, as it will cripple virtually any switch in now that Z-Moves and Megas are not in the game. This is still a very interesting option, but it should be treated with caution.
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Ghost-type is interesting, its main moves don't really give us access to any status effects but Hex has good synergy with other status moves, which could serve as a great incentive to run them. Unfortunately, if we go this route we'd have to compete against Dragapult, which commonly uses this same strategy. We could still differentiate ourselves from it with an unique secondary typing, but I think there are better ways to achieve our concept without directly competing with one of the best Pokemon in the metagame.
-A
Water-type has merit, but I feel like having to deal with the all the immunities makes this rather underwhelming on the offensive side, especially given these immunities can negate Scald burns, which would otherwise be a fantastic selling point. It is still very workable, but this wouldn't be one of my first picks.
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Normal- and
Ice-type are good offensively, but are really hard to support on the defensive front, as they offer virtually no resistances. Normal-type's immunity to Ghost-types is probably its only significant defensive use, but I don't think that's enough to justify having nothing else. A good secondary type could make them salvageable, but even then, I feel like there are better options.
-On the opposite end,
Steel-type falls behind in the offensive side significantly. Its main selling point would be nailing Clefable, but it really doesn't do much else and it won't stand by itself, although again, it might be worth considering if it complements another type well.
Meteor Mash), or have some utility to them (ex: 
tech Bullet Punch).
