I've put a couple games down with Lylyth, herald of everblight, and I think I'm getting a feel for her. At a glance, she's a support caster that likes to set her army up for a precise assassination run.
Stats
Speed 7 mean that she's going to be able to keep up with her battlegroup well. Bushwhack means you can shoot first, THEN take that move. Keep thatFury of 5 in mind, though. The MAT is inconsequential because you're screwing up if you're using it.
Lylyth is reasonably hard to hit, with a nice DEF 16. She's only ARM 14 with 15 health boxes, so she's not exactly durable. At least she's got six warbeasts points.
RAT 7 on top of Hellsinger is the main thing you're getting out of Lylyth: POW 12 is so-so and ROF 2 is nice, but there are two big perks: Blood Lure means your beasts can charge whatever you shoot without being forced, and Witch Mark means instead of hoping your piddly Fury 5 can hit, you can shoot the target and slap a spell on the model. Oh, and like all your beasts, you have Eyeless Sight, so you can put that arrow in someone's skull through a forest or cloud, too.
Spells
You've got a whopping three spells, which isn't a surprise: You're a friggin' 5-fury warlock.
Bad Blood is hordes-only, but if you can slap it on a target it's disgusting. If they want to leach fury from it, it's 1 damage per fury leached, and the beast ALSO can't heal, take transfers or Regenerate. If you have two spare fury and can line a shot up on a beast that looks important...this'll hurt.
Parasite is self-explanatory, and your setup spell. It's three fury to knock 3 armor off the target, and give Lylyth +1 ARM. If you want to assassinate, consider slapping this on the target. Or, if you need a hard target KO'ed, -3 ARM is basically like an average boost roll.
Eruption of Spines is a lane-clearer. It's 3 Fury, and hits the d6 closest models within 5" of your target take POW 10's. Now, look back at Hellsinger and Witch Mark. Now, remember that you want to shoot a target that a POW 12 won't kill. Or, if you can line up a shot against a low-DEF target, you've got RNG 10.
Feat
Field of Slaughter says that friendly faction models get an additional dice on attack rolls this turn.
Bear in mind that with Hordes, beasts tend to have lower MAT/RAT in order to compensate for their ability to force and throw out a HUGE number of attacks. (IE: a charging Carnivean that blows all its Fury can throw out a POW 14 spray, a PS 19 bite with a boost, two PS 16's, and then buy three more bites. Ow.). Note that Field of Slaughter is not a BOOST, but an additional die. Against high-DEF targets, you can boost the hit and throw out 4d6 to hit. That's an average of 14.5, which means even the least accurate of targets WILL hit.
Also bear in mind the sheer joy involved with high rates of fire. Beasts with sprays and anyone that can crank out a decent number of shots/swings will get the most mileage out of this feat.
If you can't arrange a knocked-down caster, this is your insurance for an assassination. In a pinch, it'll also help you clear out a great swathe of the enemy.
Warlock Summary
She's a support caster that can plant debuffs and attack spells pretty squarely on the target. Her low Fury means she probably wants a fury-management solo or two, or just some intelligent fury-management.
Experiences
I've gotten a couple of 35-point games with pLylyth so far. My force looked like:
Lylyth, Herald of Everblight
-Carnivean
-Seraph
-Seraph
-Shredder
Striders
-UA: Officer & Musician
Strider Deathstalker
Shepherd
The striders are there as a self-sufficient element that can operate on the the flank, and take out infantry. They're stupidly mobile, between Swift Hunter from the Deathstalker and a 3" Regroup movement from the UA. They also have DEF 15, Stealth, and Combined Ranged Attack. In a pinch, I suppose the high DEF can make them a tarpit in melee as well. On the downside, ARM 11 is deathly allergic to AoEs.
The Shredder is there for the joy and easy fury-management that is Tenacity, and then it turns into a guided missile.
The Seraphs are in there for versatility. Slipstream is just plain fun; who can resist pulling a Carnivean 2" closer to an unsuspecting target. That aside, a pair of them can put out a fair number of shots. They'll average 3 POW 12 shots each at 10" given Strafe (actually 1+D3 shots...), and with 4 Fury they can potentially kick out a few well-boosted shots. Combine that with the feat and you're landing 2-4 fully-boosted POW 12s on a target, which could potentially end a caster.
Failing that, the Seraphs have a PS 14 Stinger with Critical Poison, which provides an extra damage dice on living targets. It's a bonus against pretty much everyone but Cryx, and it's nice in Hordes as well.
The Carnivean is there because I wanted a beatstick. It's got a decent Animus (allowing it to go up to ARM 20) and capable of a volley of high-power attacks. If I get the chance, Slipstream can get me closer to the target and I can crank out an 11" charge, then profit ensues.
Short Version of the Battles
The wins I have so far are due to assassination. First time around, she popped her feat, slapped Parasite on eStryker, and then a Seraph charged him and ripped him in half. I don't care what youre defense is; MAT 6 + 3d6 with several swings IS gonna kill most small-based casters. Another victory, against Sorcha, went a little different: I had to clear a lane to her, which involved slapping the Eruption of Spines on a Khador Jack, then using Striders and one Seraph to open the way for the other Seraph and Carnivean to get to her, and when a Carnivean hits a half-dead Sorcha....yeah, that ends that