If I Designed Invulnerability

Invulnerability to me is a very straight-forward thing. The way it's depicted in City of Heroes is very mish-mashy and thematically odd: Resists, +HPs, Heal, Defense. The way it's depicted in comics is actually very simple; stuff hits you and you don't care.

If I had designed Invulnerability for CoH, it would look like this:

Tankers (all numbers assuming full SO enhancement):

Resists: Smash/Lethal: 90%; Fire/Cold: 33%; Energy/Negative: 26%; Toxic: 16%; Psi: 0%

+Hit Points: 1004 (+53.5%)

And that's it. You are all but immune to Smash/Lethal, but the further away from a "physical" attack an attack gets the more damaging it becomes until we reach the completely "nonphysical" Psi to which you are nearly defenseless (you still have a heap of HPs to help though).

The godmode would probably be +57% Resist to all but Psi on top of your existing Resists, along with 100% Slow Resist/complete immunity to mez ("Nobody can stop the Juggernaut!" lol). Endurance crash, no Health crash.

Brutes/Scrappers (I think I'm getting these right based on what Tankers get):

Resists: Smash/Lethal: 67.5%; Fire/Cold: 24.75%; Energy/Negative: 19.5%; Toxic: 12%; Psi: 0%

+Hit Points: Brutes: 802 (+53.5%); Scrappers: 716 (+53.5%)

Same godmode but with 50.25% Resist All but Psi.

The set would be pretty easily Health capped with just a few set bonuses/accolades (you only need another +5-6%). +Regen bonuses would probably be very potent and most likely the best way to IO for survivability. +Defense wouldn't be bad, though.

The only real downside I can see is even with Smash/Lethal it would only be a matter of time before you were defeated, but the +HPs, and taking Health, and getting the above-mentioned +Regen bonuses would probably cover that for the most part.