On my invuln scrapper I've had the power from lvl 28. Started in I3 and I'm lvl 50 now.. Never regretted taking the power. The taunt isnt as bad as people think, invincibility is one of the best powers of the set and should be taken as soon as possible.
- @DSorrow - alts on Union and Freedom mostly -
Currently playing as Castigation on Freedom
My Katana/Inv Guide
Anyone who doesn't take truth seriously in small matters cannot be trusted in large ones either. -Einstein
Basically you will need invincibility plus tough hide to negate the -defense from unyielding, which also may be part of teh cause why you are getting hit that much. I noticed on my kat/inv that things improved after tough hide.
You can also use invincibility for helpful defense sets, I always had it on my Inv scrapper and don't regret it in the slightest. The taunt is there to aggro melee foes on you so you can maximize your defense and your tohitbuff.
Just frustrating when trying to ghost a mish, someone casts invisibility on you and you forget to turn off invincibility 
What he said
- @DSorrow - alts on Union and Freedom mostly -
Currently playing as Castigation on Freedom
My Katana/Inv Guide
Anyone who doesn't take truth seriously in small matters cannot be trusted in large ones either. -Einstein
Thx guys, I'll get it now at lvl 28. I'll see how it goes, remembered I have a respec available, so I can swap some powers if I need to get Aid Self sooner. Also I'll see how much I can annoy tanks 
Atm doing Croatoa arc and I burn very nicely. I had fun with my SR scrapp, but with inv I'm pretty annoyed.I hope will pay off in PvP all this stress, because this toon is for pvp.
The -4% defense from Unyielding will still remain for Melee, Ranged and AoE thou'. On all others(fire, cold,etc) will compensate like you, Nightmarer say. Or it can remain -2% using combat jumping .. or compensate totally with stealth, but I'm not interested in those. There are also bonuses to compensate from, still long way until there.
I've read your guide DSorrow, nice guide for PvE. In my opinion Presence will go much better for PvE and PvP also. I'm using Provoke/Invole Panic on my PvE pseudo-tank SR build and well I can tank. I'm sure will go even much better with invulnerability. For PvP It's hard to use SJ vs others fly, unless you take web grenade or you have smth like Impale from Spines power set for -fly(which I don't have on claws).
Hehe, the -4% for Melee, Ranged and AoE doesnt matter at all really if the typed defences are over that. Remember, the def is always calculated for the highest defence factor. Say, if someone attacks you with impale and your defence stats are:
10% for Lethal
0% for Toxic
-4% for Ranged
You will have 10% defence against impale because it's a lethal/toxic ranged attack and your highest defence factor against it is the 10% against lethal.
And for the presence pool.. That's just my personal opinion. Didnt like it much for pve because some powers are much better and more needed 
- @DSorrow - alts on Union and Freedom mostly -
Currently playing as Castigation on Freedom
My Katana/Inv Guide
Anyone who doesn't take truth seriously in small matters cannot be trusted in large ones either. -Einstein
What it does mean is pure toxic damage will have a higher chance of hitting you because there is no typed defence for it only positional
"Well, they found my diary today.
They were appropriately appalled
at the discovery of the eight victims
They're now putting it all together.
Women wrapped in silk
with one leg missing
Eight legs, one body, silk,
spider, brilliant!"
[ QUOTE ]
In my opinion Presence will go much better for PvE and PvP also. I'm using Provoke/Invole Panic on my PvE pseudo-tank SR build and well I can tank. I'm sure will go even much better with invulnerability. For PvP It's hard to use SJ vs others fly, unless you take web grenade or you have smth like Impale from Spines power set for -fly(which I don't have on claws).
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I had Presence Pool on my Kat/Inv scrapper for a while on an experimental build and I respecced it as soon as I could. The duration of the fear in Invoke Panic is pants and so is the Taunt effect. If you want a taunt in your scrapper, Confront will do much better. Also, if you need a -fly power, Air Superiority is great and allows you to get Body Mastery, which probably will be better for PvP (Focused Accuracy / Conserve Power)
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For PvP It's hard to use SJ vs others fly, unless you take web grenade or you have smth like Impale from Spines power set for -fly(which I don't have on claws).
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While it may be hard, its entirely skill-related issue I think. I have never had much trouble to combat fly with SJ, unless they are purposefully escaping.
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Basically you will need invincibility plus tough hide to negate the -defense from unyielding
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This isn't entirely true, since scrapper unyielding debuff value was changed so it is in line with scrapper tough hide. It used to be true though but that was long time ago.
To the OT, you can never overrun Tanker taunt with your own invincibility taunt, so keep that in mind
Tested Invincibility. IMO - a 5 star power. It's the power that saves this set from being nasty to play (until Unstoppable). I had a 50 regen, have a 50 SR and I dunno I wasn't been ok with the idea of taking almost all the hits, stay in almost red and then use dull pain.
With Invincibility and dull pain properly slotted and used, inv scapps are fun to play, of course if you have the right foes to face 
With SR you escape sometimes a lot of hits and then all the attacks hit you, (it's like a "compensation" ) and in those moments without being used to watch your health you faceplant. Of course I'm making a parallel for these lvls, below 30s.
After you get Invincibility, the way to play is to go in the middle of the mob, of course you don't have to be over zealous at these lvls. I go in mishs with my pockets 2/3 full of "greenies", my faceplant salvation. After 30 and Aid Self, the fun will be longer.
And yes auto taunt from Invincibility isn't as bad as I thought. As you said I can't overrun the tanks taunt (BUT I haven't teamed with an inv tank using only Invincibility to taunt - I'm curious how will go then).
Still, feels great to steal the food of other scrapps, bringing foes around you. Not great when you are almost dead. Took as many AoE attacks as I could until now to hit as many as I can in the same time.
Also I feel bad for blasters who can't keep their hands off AoE blasts in teams where I have to pseudo tank. After they blast and push the mob all over the place I am not responsible for them. They "overrun" my taunt, so keep than in mind, you blasters if you have a pseudo tanks inv scrapp in your team.
I must say, maybe in that way they save my butt sometimes, being out of dull pain and greenies, but this means in some cases their doom.
Cant's wait for Unstoppable.
So to conclude, taking Invincibility at lvl 28 is the best idea.
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What it does mean is pure toxic damage will have a higher chance of hitting you because there is no typed defence for it only positional
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Not exactly, if you have 10% def to ranged and 5% to lethal, the calculations will only take in the 10% def against ranged.
All of the def checks only, ONLY use the highest defence value available.
- @DSorrow - alts on Union and Freedom mostly -
Currently playing as Castigation on Freedom
My Katana/Inv Guide
Anyone who doesn't take truth seriously in small matters cannot be trusted in large ones either. -Einstein
Yes, but he's talking about pure toxic damage - not an attack with a mix of toxic and lethal.
I'm playing a claws/inv scrapper, atm lvl 27.
Invincibility is a very nice power, gives you a base defense of almost 5%(scrapps) and also defense and tohit bonus for every foe near you (up to 10 foes) BUT has taunt in it with same base taunt effectiveness which a tank has . Power is available at lvl 28.
I'm using Dull Pain (3rech/1heal slotted so far, Self heal is a must also in the near future.
So far I find myself very squishy (except for melee foes(smashing,lethal)- because it's my specialty having much higher res to those) and I'm like a lamb for elemental/energy foes (elemental,energy/negative res provided way too small).
I'm thinking that auto taunting with Invincibility, I'm going to to die very often at these lvls and also I'll interfere with tanks herding/aggro. I'm usually stay near tank, he tanks, I kill, but when in mob is a boss kicking us from the distance, I jump over the taunted mob straight to him. Oh well with my Invincibility on I think I'll aggro that mob on me, until and IF tank taunts again. Also most of the tanks out there, around my lvl are inv and ice using only taunting aura -> so .. in this case I'm so dead.
Instead of that, I was thinking of taking Aid Other at 28, Aid Self at 30 and Invincibility at lvl 32/35.
On the other hand I don't know how well I'll handle damage until lvl 35 only with dmg res provided by Unyielding, Temp Invulnerability and Resist Elements
So, is it a bad idea to take Invincibility at lvl 28, especially before taking Aid Self? Should I leave it for lvl 35+?
Note: Very rare I end up teaming with good healers so I can't depend on them saving my butt.
Any advices from invulnerability scrapps are most welcome.
Thank you in advance!