Invuln is a pretty good set now. it's relatively weak against Psi, but then again only a few sets have good psi res anyway. I have an Invuln scrapper and enjoy playing her but in order to get the best out of her I really have to be 'in their face'.
First thing you do when you approach a mob is find the best way to get right into the middle of them. makes you seem a little suicidal at times but nipping away at the edges of a mob will get you killed. you need bad guys around you to make you harder to hit. Because of your taunt aura sometimes it can be a bit of a bind, especially around AV's and heroes if there's no tank in the team. other than that it's a slow burner and takes a good while to get 'good' in terms of the powers.
Defiant 50's
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@Miss Chief
Been playing a invul brute lately and the only downside is the late mez protection. Odd thing is though is i currently have a slight problem with big bursting s/l(ss mooks, council bosses, snakes) enemies at relentless but that should be solved with so's.
Invulnerability is a good set with good to excellent mitigation, depending on damage type and environment.
Peak performance after suitable power choices and slotting IO sets is very good. The set does however need a while to mature. Lower level play (below 20) can be frustrating at times, especially so before Invincibility is available.
Invulnerability is also somewhat slower to recover from damage or exertion than some other sets, as it does not have extra recovery or regeneration. This differs from Willpower.
As for PvP performance, it can work very well if the build is good. It benefits from added resistance (Tough), defense (Weave, Hover, Combat Jumping, IOs, et.c.), regeneration (Health, IOs) and recovery (Stamina, IOs). As always, Aid Self is highly useful if you can fit it in, have the recovery to use it and can stand the animation (personally I can't, but opinions vary). I would personally recommend focusing on extra Defense for a PvP build.
One piece of information I have found important to remember is that Invulnerability relies on both resistance and defense to stay alive. Neglecting either will make it much less effective than it could otherwise be.
I just found this thread on the US scrapper forum. It makes for an interesting read on Invulnerability and what you can do with it.
Invul is a great set. Aim for high defense, and get Tough, to get the most out of it.
Both my main villain and hero alts are Invulnerability (Brute and Tank). I've had great fun with them both, my Tank especially. Though as mentioned above it's a good idea to focus on both Res and Def to get the best performance, getting Tough and Weave will certainly help though imo you'll need to keep an eye on your endurance but good slotting should eliminate that problem. Reminds me of when Mother's Love and I were in PI fighting GMs, quite a sight watching an invulnerability Tank foot stomping over 8 GMs so there's a lot of potential in the set if slotted right
Invulns great with mobs around you. But if you've been unfortunate like me you would of found that 99% of the people in game think that mobs stopped away from you is saving you...well...okay everyone hates me 
He will honor his words; he will definitely carry out his actions. What he promises he will fulfill. He does not care about his bodily self, putting his life and death aside to come forward for another's troubled besiegement. He does not boast about his ability, or shamelessly extol his own virtues. - Sima Qian.
Yeah invulnerability is awesome for taking damage, and invuln has recently been updated with a few more resistances. You should get the most defence you can get out of invuln so make sure you get the right set bonuses. For instance Aeigis a resist damage IO set provides some good defence.
I liked it at first, but I stopped playing my Inv brute at level 33 and rolled a WP brute instead. WP manages end so much better, and for me it's more fun (it also has fewer mind-meltingly ugly auras). Inv brutes can take a certain amount, but the endurance drain is a pain, and once the damage veers away from s/l it's a hard world - and in the 30s, the foes have largely moved on from simple s/l damage.
It's all very well holding forth on matters to do with set bonuses, but really - apart from those with a bazillion inf accumulated on all their level 50 farm toons, who can afford a range of adequate sets?
The IOs in question that give the damage-type +Defense bonuses that're aids to survivability aren't too bad in cost though, really, for Invulnerability.
The main staple to bring defenses up are the Steadfast: Res/Def unique, around 15-20 million, Reactive Armour for it's several damage-type defense set bonuses and your choice of taunt sets. All of the taunt sets are dirt-cheap I believe, would lean towards going Mocking Beratement myself, and I'm pretty sure Reactive Armour is very cheap, too.
Invulnerability is a late bloomer, though. As a primary it is, as a secondary even more so. It does however have exceptional potential, even if it's hard to get into.
Reactive Armor is dirt cheap, often pick up and craft a set for less than 3 million inf (a full set that is, don't have any full sets on my invuln/ss).
Mocking Beratement is dirt cheap, pick up the entire set already crafted at about 5mil inf or less.
Thunderstrikes are very good for raising def and are a middle price range IO set, just shy of 10mil inf putting them in the same price range as Crushing Impacts.
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A real showstopper!
For the S/L variety (yes it -is- worth getting high S/L defense because of the sheer amount of pure or partial S/L damage out there compared to everything else), Kinetic Combat is good, though the price has skyrocketed since i13. 
What's it like? It any good for pve and pvp?
I heard since i13 it is a lot better, what's it better for, more resistances or something?
So is invulnerability any good? I heard some invulnerability scrappers and tankers soloed the positron tf (eventhough you need 3 to start)
And I heard brutes with invulnerability is a well wanted brute to tank for teams, and I heard they have soloed AV's pretty easy
Is it any good, mainly for brutes as I wanna make a invuln brute
And I am thinking energy melee would go nice with it