Have Torrent, Gloom and TT on my DM/SR. I use TT to stack with MG to imob things, Torrent very rarely and Gloom quite often cause its fairly nice. Nightfall wasn't an option when I picked it up but I wouldn't have room anyway
"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!"
Between Nightfall and Tentacles, the Dark Mastery set has some very respectable cone damage capabilities; something that you may be especially interested in due to Dark Melee's single target-heavy nature. You also get more of the -tohit, which pairs nicely with all the Defense you get from SR.
My only concern would be the frequent repositioning to maximize the cone attacks. That's a lot of jumping into/out of a fight. If that doesn't bother you then I think you'll enjoy the set.
You can either work the powers for damage (Soul Drain + Nightfall + TT = Yum), or use them to slot IOs that benefit the rest of your build. You could even have some fun and slot the Chance to Hold Proc from the Gravitational Anchor set and spam TT for some really nice crowd control.
I'm not a huge fan of Torrent personally, only because I don't like having to chase my prey down. Tentacles is one of the few immo powers that doesn't have -KB baked in to it, so it wont stop Torrent from flinging your nicely grouped mob to the four winds. If you like to go Hellion bowling or don't mind the KB (say, as an extra defense measure), then by all means, have fun with it. 
My personal picks from the set, as a Dark/SR Scrapper would be: Pet. Gaze, Nightfall, Tenebrous Tentacles. Skipping Torrent unless you really do enjoy knockback (it's mag 10! Watch them fly!), and skipping Dark Blast simply because you generally have better single target options available to you. It's certainly not a bad power though, in my opinion.
Quick little Point of Order: Scrapper Darkness Mastery doesn't get Gloom. Scrapper Darkness Mastery gets Dark Blast.
The difference?
Dark Blast does 62.56 Neg Dam with a 5.625% ToHit Debuff
Gloom on a scrapper would do 110.11 Neg Damage with a 5.625% ToHit Debuff
While Nightfall and Tenebrous Tentacles are both cones, anything that will help out Dark Melee's lack of AoE damage sounds like a good thing.
Be well, people of CoH.
I took the three cones on a dm/da. They're all six-slotted, and so far I am finding that the repositioning makes them less useful than I expected. It helps a lot if you fight from hover and can just go up after Soul Drain, ctrl-tab to target the nearest, then let the cones loose.
Mostly the use I get out of them is concept plus just having ranged attacks on a team, so I have more options. Also, Torrent is oddly useful as an opener to flatten a group up a bit, then charge in and they wind up more bunched than they would have been otherwise.
Virtue
Angel Witch II - Chord of Souls - Storm Witch II - Princess of the Dawn - Standing Horse - Witch of Xymox
Silent Scream - Shadow Witch II - Liquid Serenade - Nebulous Dawn - Ghost Witch II -Xiberia
Angel Witch II - Chord of Souls - Storm Witch II - Princess of the Dawn - Standing Horse - Witch of Xymox
Silent Scream - Shadow Witch II - Liquid Serenade - Nebulous Dawn - Ghost Witch II -Xiberia
For getting the most out of your Cones, especially when getting dogpiled or the power has knockback ... consider simply jumping straight up ... and then at the top of your jump, use your Cone attack(s) pointing down at your selected target. This little tactic will turn your Cone into a PBAoE(ish) attack that can hit everything that clustered up around you on the ground where you'd been standing.
I use this tactic all the time on my Ice/Ice/Arctic Tanker in order to deploy Frost to greatest effect. Simply hop straight up and at the top of the jump, use your Cone attack.
If you can jump higher than the Cone attack has range for, it'll simply cue the power and automatically attack when you reach the Cone's range on the way down from your hop.
No fuss.
No muss.
It's the end. But the moment has been prepared for ...
I have it on my seldom used alt build (fun build but can see the age in it) for my claws/SR. I grabbed it at the time part as it would let me slot 3 more purple sets (ranged, hold and immobilize) and get the recharge bonuses. Mobility was not an issue for using them, as in addition to CJ and Swift she has 5 GotA +7.5% slotted, Hover plus Quickness, in a word extremely mobile. And yes seeing the Gravitational Anchor proc is fun.
Thanks for all the replies.
I'm going to skip Torrent b/c of the KB, so will be taking Petrifying Gaze instead, and I want the Tentacles. Would Dark Blast or Nightfall be a better option? Are they good as attacks, or used more as set mules?
I had dark blast (and torrent for the "shove" move) for a while then spect out of DM completely to Pyre for concept reasons. The cool thing I liked (IDK about performance in this case) is that blast travels rather slow, so I would hit it and run into melee range and stack 2-3 attacks for really good damage. Was really fun. (I also do this with Energy torrent and LBE). Also, as you referenced, I used it then, and now fireball, to mule the apoc set.
TBH and on a performance note, I dont care for any of the attacks and find that I use a particular pool based on what I can mule and concept purposes- pick what u want and what will be fun.
Miss Arc #147491: Rise of Bedlam
AKA Iron Smoke @Champion Server
Thunderstrike in Dark Blast is fairly essential for my build, but then could have that with any epic.
I guess the benefit of Dark is you can use -tohit and Imob IOs too if you're just muling
"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!"
I have a DM/SR Scrapper that is still has a way to go til 41, but I am planning to pick up Dark Mastery, for concept reasons. I was planning to pick up Petrifying Stare, Gloom/Nightfall (one or the other) and Tenebrous Tentacles.
I believe Dark is one of the lesser used Epics, and I only looked at the stats briefly, but that other than maybe Gloom, the powers seem rather underwhelming. Has anyone had any experience with them, and can tell me how good/bad they are, or if there is synergy with DM/SR? I will likely end up taking Dark anyway, to try it out, but any information on what to expect is appreciated.