PttP's leading question was all about Aegislash, so that's what I'm going to address. I've been teetering on the fence about Bulletproof, but recent discussions on IRC have made me believe that Bulletproof is a great Ability for CAP 18. Yes, it's an Ability that serves to defeat only one set on one Pokemon, but that one set happens to be both arguably the best set on any Pokemon in the metagame and unarguably the most threatening set to our core. Furthermore, there is no other step in the process where we can deal with Aegislash as well as we can during Primary Ability. Aegislash is a great Pokemon because of its tremendous Special Attack to go along with its Attack and because this metagame is much, much better equipped to handle Physical attackers than Special attackers.
Right now our core has two Pokemon that provide free switches to Aegislash. I would be hard-pressed to justify using Lucario on my team when its absolutely shut down by Aegislash, but would be much more confident using it if I could pair it with an amazing Aegislash counter that can bust through the Pokemon Lucario cannot defeat that other sweepers can. Not only that, but a Bulletproof CAP18 both takes advantage of Latias' Defog support and handle its top switch-in.
If we force Aegislash to run Shadow Claw over Shadow Ball, that is a massive victory for the core. Although it doesn't make our core any better by itself (Physical Aegislash destroys our core almost as easily as Special does), it makes our core significantly better in the context of its team. Physical Aegislash is not very good in this metagame. It's hard-stopped by Intimidators, usually needs Life Orb to achieve the power it needs, and is therefore significantly less durable. If we're forcing Aegislash to run Physical sets, it makes our core much more enticing to use on a team.
Right now our core has two Pokemon that provide free switches to Aegislash. I would be hard-pressed to justify using Lucario on my team when its absolutely shut down by Aegislash, but would be much more confident using it if I could pair it with an amazing Aegislash counter that can bust through the Pokemon Lucario cannot defeat that other sweepers can. Not only that, but a Bulletproof CAP18 both takes advantage of Latias' Defog support and handle its top switch-in.
If we force Aegislash to run Shadow Claw over Shadow Ball, that is a massive victory for the core. Although it doesn't make our core any better by itself (Physical Aegislash destroys our core almost as easily as Special does), it makes our core significantly better in the context of its team. Physical Aegislash is not very good in this metagame. It's hard-stopped by Intimidators, usually needs Life Orb to achieve the power it needs, and is therefore significantly less durable. If we're forcing Aegislash to run Physical sets, it makes our core much more enticing to use on a team.