It's a lot easier to stack defense in this game than it is resistance, so if you're gonna go for a high survivability build, defense is the correct choice, especially since you don't have mez protection unless you're traps or sonic res. If you're a trapper, Scorpion Shield is the best bet. If you're /sonic, then a res shield would do you best.
If you're anything else, I would still suggest Scorpion Shield.
My Dark/Cold prefers Soul Mastery, to snag [Power Boost], the debuffs really shine with it.... which leaves [Dark Embrace] for resistance rather than defense. At least it picks up Toxic resist that way.
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By itself you won't notice much protection. When something gets past defense, you get all of it and Scorpion Shield slotted will only add about 20% smashing/lethal and 12% energy. Even-con minions will still hit you 30% of the time, which is better than 50% of the time but not by much.
Whether you go defense or resistance they are best when stacked. Defense stacks with more defense and, effectively, also stacks with tohit debuffs on your foes. Dark primary and secondary as well as Rad secondary are great with Scorp Shield. It'd be almost overkill with a Dark/Dark corruptor but I use it on my AR/Dark together with defense stacking from CJ, Shadow Fall, Maneuvers, and IO bonuses. If I start a fight with Darkest Night or Fearsome Stare, most of what shoots back will be doing so with floored tohit chances. And when something hits, there's a big heal waiting. You don't want to rely on defense without it because even at the tohit floor, the things most likely to get past your defense are also the most likely to be coming from heavy-hitters who can put you below half health easily with one shot.
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Thanks for the info so far! I am Fire / Kin, probably should have mentioned that earlier 
I have Maneuvers currently, so it looks like between that and Scorpion Shield, once properly socketed, I should be able to get around 25% DEF? I have some minor set bonuses that add DEF as well, but nothing huge. I normally duo with a Brute friend so I'm not often the target of all the mobs, just when Fulcrum Shift or an AE attack pulls something onto me (unless I do something silly, which can happen).
My current problem is more to do with status effects than outright damage. I recall a particular series of missions against Longbow, their Nullifiers would stand back just out of aggro range of the Brute, and once I'd launch an attack they would turn on me...one shot, and I'm stunned...over and over heh. It sounds like giving the Nullifier a 25% greater chance to miss would be good.
I might give Scorp Shield a try! If nothing else I have some respecs burning a hole in my pocket so I could recover from it if it turns out to be bad. Thanks for the feedback!
One other question maybe someone could help out with .... I'm wondering what the various powers look like, so as not to entirely destroy my char concept. Is anyone aware of any web sites that would give me an idea of the graphics?
Thanks!
25% smashing/lethal defense will cut in half the damage you take from even-con minions who deal that kind of damage. So that includes most melee attacks as well as most guns (flamethrowers and void hunter rifles and such being exceptions) and even most ice bolt type attacks since they do both cold and smashing. If any part of the attack does smashing or lethal, you'll have decent protection. A bit less for purely energy-based attacks and pretty much just the 5% from maneuvers for anything else like fire/cold/psi.
That's if nothing else is in play like tohit bonuses on them or defense debuffs on you. Unfortunatey enemies with guns typically do debuff defense. Longbow, Council, Family, etc. You might want to put lethal defense in your monitor window so you know when you've been heavily debuffed. Course... getting hit all the time is another indication.
As for power animations. I don't know of a site offhand that shows them. Scorpions Patron shield is pretty light on graphics. You'll notice a faint purplish aura but that's about it. The patron shields occasionally flash a glyph that supposedly is unique to each patron but that's also pretty understated. Activating the shield is a similar animation to Hasten, but without the firey hands effect. You get some pulsing energy field kind of effects and then they subside.
Scorpion's Web Envelope uses the Arachnos Mace, which you can customize a bit if you want at the Tailor. You draw the mace and hold it two handed pointed at your targets and the grenade fires, with the web strand effects showing up briefly around your targets and then staying there if the immob affects them. Similar animation with the hold. Summon Disruptor is fairly self-explanatory if you're into pet summoning. Arachnos mechanical spider blaster thingy. Noisy.
Ghost Widow's powers mostly resemble things you'd see in Dark Armor or Dark Miasma powersets. Soul Storm, the hold, is fairly unique though and picks up the target, spinning them in the air with white energy streamers swirling around them. Very much a magic themed effect.
Scirocco is all about the Mu red lightning and Mako has you throwing fish at people. It's really kind of ridiculous looking.
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I think spirit shark is one of the best looking animations in the game. I do agree that the concept of throwing fish at peeps is almost like an inside dev joke. They should have ghost widow throwing kisses, scirrico throwing scrunchys, and Black scorp throwing hot dogs...
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I was hoping to get some feedback from people that have experience with the various ancillary powers available to Corruptors. I'm level 40 currently, so I guess it's time I looked into this!
I was fully planning on getting one of the powers that adds damage resist, but then I noticed that Scorpion Shield adds defense? That *sounds* like a great idea to me, but I'd like to hear from others that have tried it to see how it actually plays out.
So, anyone out there willing to share a story of how they think these powers add to survivability?