Just a couple things; You'll want a little more acc in dark pit, fearsome stare and you'll also want at least one in fluffy, no point slotting heals and holds if he cant hit anything 
Also i think you'll need more end red across the board. HT in particular is very costly, and 2 end in shadowfall.
I'd suggest a slotting of 2 acc, 2 recharge, 2 tohit debuff in fearsome stare. Apparently it has the same base debuff as DN, and is perma without fear duration and is already a huge cone.
assault as lvl 35 but no tactics? i wouldn't bother, bit of an end drain for little return. I find recall friend is handy, esp for stealthing, which you can do running SF and SS.
No major mistakes though, just tweaks...enjoy your uberness 
I miss him in the weeping of the rain;
I want him at the shrinking of the tide;
The old snows melt from every mountain-side,
And last year's leaves are smoke in every lane;
But last year's bitter loving must remain
~Edna St. Vincent Millay
It's just so hard to get all the slots in early... :S No idea as to priorities.
Okay, I'm making a dark/dark to be very team friendly, with as much control/debuffage as possible, and I've come up with this build. This is for PvE
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Exported from Ver: 1.7.6.0 of the CoH_CoV Character Builder - (http://sherksilver.coldfront.net/index.php)
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Name: Dark Spirit
Level: 50
Archetype: Defender
Primary: Dark Miasma
Secondary: Dark Blast
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01) --> Twilight Grasp==> Acc(1) Heal(3) Heal(5) Heal(31) Acc(40) Rechg(40)
01) --> Dark Blast==> Acc(1) Dmg(3) Dmg(34) Dmg(34)
02) --> Tar Patch==> Rechg(2) Rechg(31) Rechg(36)
04) --> Darkest Night==> TH_DeBuf(4) TH_DeBuf(5) TH_DeBuf(7) EndRdx(25) EndRdx(37)
06) --> Howling Twilight==> Rechg(6) Rechg(7) Rechg(9) DisDur(9) DisDur(19) DisDur(36)
08) --> Swift==>
10) --> Dark Pit==> Acc(10) Rechg(11) DisDur(11) DisDur(15) Rechg(36) Rechg(37)
12) --> Fearsome Stare==> Acc(12) Rechg(13) Fear(13) Rechg(15) Range(43) Fear(46)
14) --> Hover==> Fly(14)
16) --> Tenebrous Tentacles==> Acc(16) Dmg(17) Dmg(17) Dmg(19)
18) --> Health==> Heal(18)
20) --> Stamina==> EndMod(20) EndMod(21) EndMod(21)
22) --> Night Fall==> Acc(22) Dmg(23) Dmg(23) Dmg(25)
24) --> Fly==> Fly(24)
26) --> Shadow Fall==> EndRdx(26) DmgRes(27) DmgRes(27) DmgRes(29) EndRdx(37)
28) --> Hasten==> Rechg(28) Rechg(29) Rechg(31)
30) --> Super Speed==> Empty(30)
32) --> Dark Servant==> TH_DeBuf(32) TH_DeBuf(33) TH_DeBuf(33) Heal(33) Hold(34) Hold(46)
35) --> Assault==> Empty(35)
38) --> Blackstar==> Acc(38) Dmg(39) Dmg(39) Dmg(39) Rechg(40)
41) --> Oppressive Gloom==> Acc(41) Acc(42) DisDur(42) DisDur(42) EndRdx(43) EndRdx(43)
44) --> Dark Embrace==> DmgRes(44) DmgRes(45) DmgRes(45) EndRdx(45) EndRdx(46)
47) --> Soul Drain==> Acc(47) Rechg(48) Rechg(48) Rechg(48)
49) --> Petrifying Gaze==> Acc(49) Hold(50) Rechg(50) Hold(50)
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01) --> Power Slide==> Empty(1)
01) --> Sprint==> Empty(1)
01) --> Brawl==> Empty(1)
01) --> Vigilance==> Empty(1)
02) --> Rest==> Empty(2)
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Any screw-ups?
And I am using dark pit and howling twighlight as control. I personally like them