I play Invulnerability and Dark most often on Defense sets. I use Hyperstrike's Invul templates. I will not go into details, because everything I do there is pretty much plagiarism
Dark. Hmmm. Many people on the boards F this up so bad it just makes me shake my head. They do not take either / or both Stun and Fear Toggles. For whatever reasons. Shit decision. Everybody that knows anything about Defense sets in CoH knows this: Defense is better than Resist is better than Heal. Simple Math statement. Def > Res > Heal. Dark is a Resists set, so should be in the 2nd tier, at best. Built correctly this is not only an A tier set, but in most cases an S tier set. I have Tanked Rom on a Master Ms Lib run using Dark successfully. So, why? First. DO NOT try to build Defense. You have no Defense Debuff Resistance. Build Resistance. But you point out, didn't you say Resistance is less effective than Defense? How does that work? So... I tell you. Dark stands Def > Res > Heal on it's head and then dances on it's feet. Dark has non suppressing Stealth. So you can brutalize 17 Longbow and their buddies in the next spawn a few feet away stand around, drink coffee, and idly wonder what is going on. Dark's Stun, Fear, and To Hit debuffs provide a VERY strong "faux defense" to STOP attacks so you do not need Def, Res, or Heal. This works on the trash. On beasts like Rom and AVs? You can get most of your armors at 100% Res easy. This means they cannot be debuffed. Res will cap at 90% but Res is it's own Res debuff Res. 100% works against everything but a few weird LB wardens with a special power. You cannot get Energy to 100, but you can get it very high if you try. Hard. So you are mostly taking tiny damage from everything that does hit you. Then Rom wallops you with ALL the energy damage. But you got high (if not perfect) energy resistance... AND... the best heal in the game. Hands down. No contest. Take you from 1% to 100%. and it is up every few seconds. Dark. Not for everyone. Expensive. Tough to build right. Tough to understand at first. S class armor just waiting for you to try.