Stick with the 15 point list for the moment. Remember that Nightmare is stealth whilst in Deneghra's control area and take advantage of that by moving around your opponent's threats. Prey a jack or solo that will be ahead of the caster as then you can use the movement bonus to get your claws on the opposing warcaster. With Deneghra1's feat/spells you won't need the prey bonus to hit/kill. And if you kill the prey target then switch to the warcaster.
The arc nodes are the way to keep Deneghra back from the front line but don't worry about losing them. Say the opponent has two heavy jacks, get one arc node within 8" of both and cast parasite on the front one and crippling grasp on the back one. With the -3
ARM nightmare will rip it to shreds. You can even wait a turn just out of threat range so that he can go in fully fueled with focus. And you don't need to worry about the rear one taking out nightmare as it'll be -2
SPD and can't charge nor hit you. Even if you lose that one arc node you have a spare that is free and can move around to the back field to arc venoms on the squishy stuff at the back.
The Warwitch Siren is a great piece as you should be giving out one free focus to the nearest arc node then using that to run it without investment from Deneghra. Or if you have crippling grasped a heavy then charge in with her sword and shadow bind the big guy. Especially if it doesn't have reach as you can stay out of melee range and the jack can't do anything to you.
What I would be doing in the game is deploying and setting up the prey target. Nightmare and Deneghra in the center(ish) with the arc nodes either side between 6"-14" away from Deneghra and the warwitch siren picking a side that has less terrain in the way (lack of pathfinder means that her best defence is stealth).
1st turn; allocate focus to the jacks, one each and run the arc nodes behind forests/cover something that either blocks
LoS or boosts their already high defence. Run Nightmare up about 10" or so. Enough to be a threat but not so much that he can be hit by the enemy. Then move Deneghra up so that she's close behind Nightmare and has at least one of the arc nodes in control range. If you have one outside control then get the warwitch siren close to that one and then you can get it back into control range next turn to cast spells.
2nd turn; you are likely to lose one arc node this turn but that's ok. Measure control range from Deneghra and decide if you want to get nightmare in combat. If so you'll only be casting one spell this turn and thus feel free to give Nightmare some focus so he can kill whatever you need. Activate the Siren and give the closest arc node a focus. Run that into spell range of the enemy (if you don't need to run then by all means shoot it's gun using the focus to boost hit or damage) Activate Deneghra and move up to get that arc node into control range and cast Crippling Grasp or Parasite on the target of Nightmare. You could even feat if you can get Nightmare within reach range of two big targets. Take down the preyed enemy first and switch to the next model to put the hurt on it.
Of course you might not be able to get Nightmare into combat so you'll want to use that arc node to get both Parasite and Crippling Grasp on those targets. You will deffinately lose that arc node but with both those spells out there the battle has become much easier for you. Upkeep next turn and kill with Nightmare fully fuelled with focus and Deneghra's feat if you think it best.
At this point I can't help any more but you should have eliminated a large threat or two and be ready to carve up the enemy caster.
Some else to try out is;
Get an arc node within 4" of a high defence target (especially casters) and cast scourge. Everything under the template is knocked down and you can't scatter off the target when the point of origin is within 4" (
here). Boost damage if you hit and kill with ranged shots/Nightmare.
Edit:
Forgot a couple of things. Dealing with infantry is easy with venom. You can have 4 of these sprays a turn with Deneghra and the Warwitch Siren. POW 10's will destroy most infantry and if it is
ARM 17+ or multi wound then you can get crippling grasp on the unit and effectively remove them from the game. Hard to hit? Then feat first before spraying.
On to the 25 point level. Put in Gorman and you have 8 points to spend. A mininium unit of bane thralls +
UA is 8 points. Max Satyxis Raiders. Max mechanithralls with a necrosurgeon and brute thrall. Basically choose an infantry unit and use that to get you up to 25pts. You don't really want to put more jacks with Deneghra as a heavy and two arc nodes is very close to the limit without extra resources.
Finally, if you want to use the pistol wraith then use two of them at once. Yes, it's a heavy point investment but with two of them you can get souls from nearby infantry and use that later to boost damage on a knocked down caster (remember scourge) or take out easy to hit heavies with the death chill. If you really don't like a heavy then blind with gorman and then death chill. That heavy can do absolutely nothing next turn. One of them is easily ignored, two and you have a hard to take out threat.
