Don't have much to add to what people have already said, so will keep this short.
In terms of us needing to toe the line to achieve the concept and not end up with a mon that drops CAP Song/is generically good, this is my order (from least complicated to most):
Lightning Rod/Purifying Salt <= No Guard (with low enough offense on base) < Regenerator (without recovery moves) <= Magic Bounce
I feel like each of these abilities lends towards very different defensive benefits, some of which can be achieved through other means as well:
Lightning Rod/Purifying Salt/Magic Bounce -> help against status, no easy way to get past this except with a suboptimal item (berry), early tera or very, very cautious play
Regenerator/Magic Bounce -> help with switch ins, only other way to get this is with team support/slow pivots
No Guard -> helps with compression with Inferno, Sacred Fire is an alternative but its 50% chance necessitates more opportunities to click it (like Pecharunt)
There has been a bit of discussion about what item we'd like to run depending on the ability. Air Balloon is definitely up there for all abilities as it provides all the benefits of Levitate and gives opportunities for early game utility/defensive function/switch in opportunity. Assault Vest has seen usage on Regenerator (Glowking, Alomomola, Tornadus) and Magic Bounce (Hatterene). Boots I think is better over Leftovers as we probably can't stay in for extended periods, but both are obviously good.
In terms of us needing to toe the line to achieve the concept and not end up with a mon that drops CAP Song/is generically good, this is my order (from least complicated to most):
Lightning Rod/Purifying Salt <= No Guard (with low enough offense on base) < Regenerator (without recovery moves) <= Magic Bounce
I feel like each of these abilities lends towards very different defensive benefits, some of which can be achieved through other means as well:
Lightning Rod/Purifying Salt/Magic Bounce -> help against status, no easy way to get past this except with a suboptimal item (berry), early tera or very, very cautious play
Regenerator/Magic Bounce -> help with switch ins, only other way to get this is with team support/slow pivots
No Guard -> helps with compression with Inferno, Sacred Fire is an alternative but its 50% chance necessitates more opportunities to click it (like Pecharunt)
There has been a bit of discussion about what item we'd like to run depending on the ability. Air Balloon is definitely up there for all abilities as it provides all the benefits of Levitate and gives opportunities for early game utility/defensive function/switch in opportunity. Assault Vest has seen usage on Regenerator (Glowking, Alomomola, Tornadus) and Magic Bounce (Hatterene). Boots I think is better over Leftovers as we probably can't stay in for extended periods, but both are obviously good.