Taken me a while to eventually come to this, can anyone spot any desperate faults?
Archetype: Defender
Primary Powers - Ranged : Dark Miasma
Secondary Powers - Support : Electrical Blast
01 : Charged Bolts acc(01) acc(5) acc(9) enddrn(31) enddrn(34)
01 : Tar Patch slw(01) slw(3) slw(15) recred(50)
02 : Darkest Night thtdbf(02) thtdbf(3) thtdbf(7)
04 : Lightning Bolt acc(04) acc(5) acc(11) enddrn(31) enddrn(31)
06 : Howling Twilight recred(06) recred(7) recred(50)
08 : Shadow Fall defbuf(08) defbuf(9) defbuf(17)
10 : Short CIrcuit acc(10) acc(11) acc(13) enddrn(37) enddrn(43)
12 : Hover fltspd(12) fltspd(13) fltspd(17)
14 : Fly fltspd(14) fltspd(15) fltspd(23) endred(48)
16 : Swift runspd(16)
18 : Petrifying Gaze acc(18) acc(19) acc(19) hlddur(43) hlddur(48)
20 : Zapp acc(20) acc(21) dam(21) dam(40) dam(43)
22 : Health hel(22) hel(23)
24 : Stamina endrec(24) endrec(25) endrec(25)
26 : Hasten recred(26) recred(27) recred(27)
28 : Tesla Cage acc(28) acc(29) acc(29) hlddur(46) hlddur(46)
30 : Recall Friend recred(30)
32 : Dark Servant acc(32) acc(33) hlddur(33) hlddur(33) immdur(34) immdur(34)
35 : Voltaic Sentinel acc(35) acc(36) acc(36) dam(36) dam(37) dam(37)
38 : Thunderous Blast acc(38) acc(39) acc(39) dam(39) dam(40) dam(40)
41 : Thunder Strike acc(41) acc(42) acc(42) dam(42) dam(45) dam(46)
44 : Charged Armor damres(44) damres(45) damres(45)
47 : Twilight Grasp acc(47) acc(48)
49 : Aim thtbuf(49) thtbuf(50)
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01 : Brawl enhancement(01)
01 : Sprint enhancement(01)
02 : Rest enhancement(02)
A few comments, mainly on slotting:
Firstly, do you think you can wait until 24 for stamina? Running DN and SF while attacking will soon run you out of Endurance. The end recovery on the attacks is not great and doesnt seem to make much of a difference to me.
Tar patch is great but you will want it up as much as possible so I usually slot 3 Recharge. Add slows to taste.
Darkest Night may need and end reduction or 2 as might Shadow Fall. Also, the defense on Shadow Fall is tiny, slotting for resists generally gives better bang for your buck.
I'm not sure Howling Twilight needs so many recharges unless you are expecting a lot of your team to die.
Do you really need 3 accuracy enhancements in all your attacks. 2 SOs will allow you to hit +3s quite well.
I wouldn't bother slotting CB and LB for end drain. IIRC they only drain 5 end per attack so you won't be getting much benefit.
The hold and immob enhancements in fluffy won't actually be used most of the time as he cycles his attacks. ToHit Debuffs might be more useful.
The above is just my opinion, ymmv.
Octavian Vanguard
@ohmsEU and @ohms 2
Badging character: Bimble on the Union server, Badgehunter.com and City Info Tracker.
Couple of points on the elec side of things (bear in mind I've got an elec blaster not a defender so please disregard anything not relevant, my only experience with playing dark is a fairly low level corruptor).
Both Zapp and Thunderous Blast have a very high accuracy, even with how late you've taken aim on there you wont need more than one accuracy in them, after you've got aim you wouldn't need any. Short Circuit also has a high accuracy, I wouldn't recommend more than one acc in that either. If you're looking for drain it takes two applications of Short Circuit to drain even level, so slotting 1 acc/3 end mod/2 recharge, or 3 recharge/3 end mod, will give you the best results. It would then be availabe about once every 12 seconds with 2 recharge or every 9 seconds with 3 if I remember correctly. I don't know exactly how much drain you'd get from two applications on a defender (it's a little higher than the blaster version) however the blaster version will do +1s with two hits so you'd get at least that.
Aim already gives a high accuracy boost but has a long recharge, you'd get more mileage with slotting it for recharge rather than to hit. I would take aim earlier, nice for the extra damage, and those moments where you really do want to hit.
As Ohms already said, you get almost nothing at all from slotting your regular blasts with endurance drain. Short Circuit has a high base drain, 3 slotted with endurance drain and you'll start to drain mobs in two hits. At an absolute outside push you may get a slight benefit from Zapp and Thunderous Blast which both have a higher base drain than the rest of the attacks (Blaster version of Zapp is 15, the defender one will be a little higher, Thunderous blast is higher again but I can't remember the figure off the top of my head) but I'm not convinced it'd be worth it. If you really want to go for drain I'd take short circuit and then eventually take power sink from the ancilliary pool to combine with short circuit.
Edited to add a little more information on short circuit now I've woken up.
I have precisly 5 levels experience with electric blasting, so I'll limit my comments to Dark Miasma.
I agree with all of Ohms advice, particularly slotting an end reducer or two in DN and SF, slotting SF for rez and slotting Fluffy for Debuffs. In addition I'd also suggest taking Twilight Grasp far, far earlier, possibly swaping it with Howling Twilight. There are two good reasons for taking it early. <ul type="square">[*]It is always useful to have a heal. Being Dark, you won't get hit much, but there's always that 5% chance that stuff will get through, and sometimes that stuff will be big. While Fluffy can heal, I really wouldn't want to rely on him.[*]It is a very, very good debuff. In addition to the staples of Darks debuffery (acc and damage) it also debuffs regen which is invaluable vs GMs and AVs.[/list]
Dead Calm's Defender Manifesto
these are just my opinions on dark miasma.. hope you find them useful..
1) its better to uterlise tar patch for the -resistance rather than the slow. the effect stacks aswell so its better to have it up asap so as people before have said slot with 3 recharge before putting in slows. i don't believe its a must have power in the early levels either so you may want to consider not taking it til mid teens.
2) get twilight grasp. its a heal (obviously you wont be an empath) but it'll save your life!
3) dont think its necessary to have 3 recharges on holwing twilight unless you want to use it as a control power but then i'd say fearsome stare is better.
4) no fearstome stare? personally i think its a great power and is always the first move i use in a fight.
5) you will need at least 1 end red in darkest night
6) swap def buff for resistance in shadow fall
7) fluffy has some kind of tohitdebuff PBAoE thing running that is very very good so slot him with some tohitdebuffs
I'd agree with Tufty here. Fearsome Stare is a great power. AOE Fear cone with more -acc thrown in for good measure. If you're mainly sticking with PvE I'd get this instead of Petrifying Gaze as it'll affect multiple enemies for you. So you should be able to floor the entire groups accuracy (and have them twitching in fear).
You know the concept of a Dark Miasma character without Fearsome Stare was so alien to me that I couldn't even notice it existed.
Get it. Slot it (I'm currently running one acc, two duration, one recharge, two acc debuffs). Love it.
Dead Calm's Defender Manifesto
You can tell I'm not the best at the whole debuffing, blasting, and secondary effects. 
As with my scrapper it was easy, 2 acc 3 dam and a tohitdebuff in most of my Dark Melee attacks. Regen, again, also very easy to slot, a few heals here and a few recharges there.
Thanks for the busload of help you guys have posted! 
EDIT: I'm not used to using cone and AoE effects that aren't PBAoE, so forgive me.
I just don't like the concept for some reason, I far more prefer hitting people near me and single targets, this is something new I am trying, tis all. 
So far this toon is lvl 11, with this build:
Exported from version 1.5B of CoH Planner
http://joechott.com/coh
Archetype: Defender
Primary Powers - Ranged : Dark Miasma
Secondary Powers - Support : Electrical Blast
01 : Charged Bolts acc(01) acc(5) dam(9)
01 : Tar Patch slw(01) slw(3)
02 : Darkest Night thtdbf(02) thtdbf(3) thtdbf(7)
04 : Lightning Bolt acc(04) acc(5) dam(11)
06 : Howling Twilight recred(06) recred(7)
08 : Shadow Fall defbuf(08) defbuf(9)
10 : Short CIrcuit acc(10) acc(11)
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01 : Brawl enhancement(01)
01 : Sprint enhancement(01)
02 : Rest enhancement(02)
I'll be changing damage in my electrical attacks for endurance modification. So I'll be a monster in PvP
EDIT: I forgot to say what I'm too stuck to choose with!
Well... I want to be as endurance draining as possible, whilst being quite damaging(both pets) and been able to hold foes(Petrifying Gaze and Tesla Cage) quite well.
Most people would call me an offender if I continued the way I wanted, because I also want Zapp.