Too tired to check it all, just gotta say, put at least one acc in Twilight Grasp.
The slotting seems OK, but you're missing one of the most useful powers, Fearsome Stare, which is worth 6 slots (mix of Acc ThT_debuf Fear Rechg). I find it more useful overall than the holds. Dark Servant can be slotted in many ways, but will need 3 Rechgs if you want it perma (unless you have Hasten, in which case 2 is enough). I don't know what the range of Web Envelope is, but I chose Soul Mastery and found that Soul Tentacles needed at least 1 Range enhance. I wouldn't bother with Health given that you have a good self-heal which as Vah said, needs a 2nd Acc, even with Tactics running, and if possible a Rechg for stacking its debuff (I don't think you need Aid Other since bots stay at range, right?). If you already chose Leadership, I would take Vengeance instead.
CoX 50s: <ill/rad> <ice/ice> <fire/kin> <grav/sonic> <ice/storm> <earth/kin> <kin/elec> <cold/psy> <thugs/dark> <fire/dark> <dark/elec> <night widow> <EM/ninj> <mind/icy>
Right first off twilight grasp should have a least 2 acc's since your going to rely on it heavily and you want to make sure that it hits every time and 2 heals and 2 recharges will ensure that you will have a steady source of heals throught the rest of your levels. With only 2 heals slotted you can practicly full heal your botts.
Tar patch i find only needs 2 recharge so you can take a slot out of that or put in a slow.
Swift not sure if you really want to waste 2 slots here since dark miasma really likes to be slot heavy to be any good.
No need for repair since you have twilight grasp and repair isnt really that good. I suggest putting shadow fall here instead.
Awssult and tactics i would recomend a second endred since dark miasma is a very heavy end build.
Assult bot take the endred and replace with dissorents since the only pets you have that have to worry about end are your protector botts which btw should have at least 1 endred.
Petrifying stare works best as 2acc, 2 hold and 2 recharge and since your getting web caccon which is slotted the same this works out brillaintly since you can perma hold boss's with the 2 working together.
Aid other you dont need either since you have the significantly much better twilight grasp. In its place either howling twilight which really needs only one slot and has great applications as a first strike move as well as a mass rez, or fearsome stare.
Shadow fall you should take a lot earlyer in your build since it really does help. Also slot another endred in it.
Dark servant Up to you on this one but its usually best to have a least 2 recharge in this one so its close to perma.
Health not really needed unless your 3 slotting guessing your using it as a filler i think you would be better off with vengance here even 1 slotted vengance is still damn usefull.
Right hope that helps you with your build. Going with the above changes will make you a monster during PvE. 
OK, I've gone back and tweaked it - minus the Patron pool this time, as I'm thinking of switching to another one, heh. Anyway:
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Exported from Ver: 1.7.6.0 of the CoH_CoV Character Builder
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Name:
Level: 41
Archetype: Mastermind
Primary: Robotics
Secondary: Dark Miasma
---------------------------------------------
01) --> Battle Drones==> Acc(1)Acc(3)Dmg(3)Dmg(5)Dmg(5)
01) --> Twilight Grasp==> Acc(1)Acc(7)Heal(7)Heal(9)Rechg(9)Rechg(11)
02) --> Tar Patch==> Rechg(2)Rechg(11)
04) --> Darkest Night==> EndRdx(4)
06) --> Equip Robot==> EndRdx(6)
08) --> Swift==> Fly(8)
10) --> Hover==> Fly(10)
12) --> Protector Bots==> Acc(12)Dmg(13)Dmg(13)Dmg(15)EndRdx(17)
14) --> Fly==> EndRdx(14)Fly(15)Fly(17)Fly(40)
16) --> Shadow Fall==> EndRdx(16)EndRdx(19)DmgRes(19)DmgRes(23)
18) --> Hurdle==> Jump(18)
20) --> Stamina==> EndMod(20)EndMod(21)EndMod(21)
22) --> Assault==> EndRdx(22)EndRdx(23)
24) --> Tactics==> EndRdx(24)EndRdx(25)TH_Buf(25)TH_Buf(29)TH_Buf(31)
26) --> Assault Bot==> Acc(26)Dmg(27)Dmg(27)Dmg(29)DisDur(36)DisDur(37)
28) --> Fearsome Stare==> Acc(28)Acc(31)Fear(33)Fear(33)Rechg(33)Rechg(34)
30) --> Petrifying Gaze==> Acc(30)Acc(31)Hold(34)Hold(34)Rechg(36)Rechg(36)
32) --> Upgrade Robot==> EndRdx(32)
35) --> Hasten==> Rechg(35)Rechg(37)Rechg(37)
38) --> Dark Servant==> Rechg(38)Rechg(39)Hold(39)Hold(39)Acc(40)Acc(40)
---------------------------------------------
01) --> Sprint==> Empty(1)
01) --> Brawl==> Empty(1)
01) --> Supremacy==> Empty(1)
02) --> Rest==> Empty(2)
---------------------------------------------
Didn't realise Twilight Grasp would be so effective as to make the other heals redundant, hence the initial slotting. This build certainly "feels" a lot tighter. Thanks for all your help, guys.
Twighlight grasp is quite possibly the best AoE heal in the game, added to that it also debuffs the target so in AV fights invaluable. Of course it does require that you stay in a tight group with your pets else some wont be healed. Am not sure how good the group AI is for bots, Necro pets quite often wander seperate ways, but for Mercs its been amazing
"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 ]
This build certainly "feels" a lot tighter.
[/ QUOTE ]
Yup i know that feeling, so many good powers in /dark that can help you just wish i could get some spare slots on my robot/dark so i can put them in to some other powers in my own build...
As for the AI botts all prefer ranged so tend to stay closely grouped together so i dont have to worry much about chasing after them, that and i keep them on a tight leesh anyway 
Alrightey, my planned build for Issue 9, currently not taking Inventions into account:
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Exported from Ver: 1.7.6.0 of the CoH_CoV Character Builder
---------------------------------------------
Name:
Level: 50
Archetype: Mastermind
Primary: Robotics
Secondary: Dark Miasma
---------------------------------------------
01) --> Battle Drones==> Acc(1)Acc(3)Dmg(3)Dmg(5)Dmg(5)
01) --> Twilight Grasp==> Acc(1)Heal(7)Heal(7)Heal(9)
02) --> Tar Patch==> Rechg(2)Rechg(9)Rechg(11)
04) --> Darkest Night==> EndRdx(4)EndRdx(11)TH_DeBuf(23)TH_DeBuf(23)TH_DeBuf(43)
06) --> Equip Robot==> EndRdx(6)EndRdx(46)
08) --> Swift==> Fly(8)Fly(37)Fly(37)
10) --> Hover==> EndRdx(10)
12) --> Protector Bots==> Acc(12)Dmg(13)Dmg(13)Dmg(15)Heal(37)Heal(40)
14) --> Fly==> EndRdx(14)Fly(15)Fly(17)Fly(17)
16) --> Hurdle==> Jump(16)
18) --> Repair==> Rechg(18)Rechg(19)Rechg(19)
20) --> Stamina==> EndMod(20)EndMod(21)EndMod(21)
22) --> Assault==> EndRdx(22)
24) --> Tactics==> EndRdx(24)TH_Buf(25)TH_Buf(25)TH_Buf(29)
26) --> Assault Bot==> Acc(26)Dmg(27)Dmg(27)Dmg(29)EndRdx(43)EndRdx(43)
28) --> Petrifying Gaze==> Acc(28)Acc(31)Hold(33)Hold(33)Hold(33)
30) --> Aid Other==> Heal(30)Heal(31)Heal(31)IntRdx(34)IntRdx(34)
32) --> Upgrade Robot==> EndRdx(32)EndRdx(34)Rechg(50)
35) --> Shadow Fall==> EndRdx(35)DmgRes(36)DmgRes(36)DmgRes(36)
38) --> Dark Servant==> Acc(38)Acc(39)Hold(39)Hold(39)TH_DeBuf(40)Rechg(40)
41) --> Scorpion Shield==> EndRdx(41)DefBuf(42)DefBuf(42)DefBuf(42)
44) --> Web Envelope==> Acc(44)Acc(45)Immob(45)Immob(45)Rechg(46)Rechg(46)
47) --> Web Cocoon==> Acc(47)Acc(48)Hold(48)Hold(48)Rechg(50)Rechg(50)
49) --> Health==> Heal(49)
---------------------------------------------
01) --> Sprint==> Empty(1)
01) --> Brawl==> Empty(1)
01) --> Supremacy==> Empty(1)
02) --> Rest==> Empty(2)
---------------------------------------------
I think I have the primary powerset pretty much sussed, but I'm unsure about slotting when it comes to the secondary. Not looking to min/max at all, but I'm wondering if you would personally be comfortable with the set-up I have going here?