the_scotsman wrote:

 Xenomancers wrote:
space marines just lose to DE on a fundamental level. Just spam stormravens and wipe the DE of the board in 3 turns. Only chance.

It's this kind of advice that breeds pointlessly fatalistic attitudes. Dude is playing a 2-patrol DE list with just a bunch of standard units with some relatively subpar stuff like Incubi. Telling someone "oh, just give up, you stand no chance" in this obviously relatively casual matchup is just ridiculous.

OP, my advice to you is going to include some list advice (because you have a few less than amazing choices in your list) and some tactics advice.

List:

-You have three sniper rifles and two boltguns in your scout squad, that's a little strange. Generally speaking, if your unit has a choice of one basic gun or another, it's almost always best to run them with all one option, rather than a mix. If your guys want to sit back and snipe, the bolters do nothing. If you get within 12" for the bolters, the sniper rifles are at -1 to hit because you're moving. I usually see scouts used for their ability to stand in front of your other marine units and block chargers, so shotguns, bolters, or close combat is usually the name of the game. If you really like the snipers, don't rip your models apart (in fact, disregard pretty much any advice to do that - the power level of every weapon in the game and every army changes, if you own only the best stuff, odds are good you'll end up owning only the worst stuff after it gets lowered in power by GW)

-Youve got a devastator squad with 3HBs and 1 plasma, and a Missile in your tacticals. Swap that puppy around, and run the devs 3 HBs and 1 missile. The stratagem "Flakk Missile" is highly valuable against Dark Eldar, since all their tanks have Fly, and the Cherub lets you reroll if you miss the shot.

-You definitely want a lieutenant and captain instead of 2 captains. gotta get both buffs going!

-Your razorback: if you have the parts from the kit to let you run that with twin heavy bolter, I would do that against Dark Eldar. Lascannons are VERY ineffective against DE, because of how wounding works in 8th edition. DE vehicle are T5, which means strength 9 is exactly the same as strength 6 against them, and they have a 5+ invulnerable save, which can block those huge lascannon shots. Twin heavy bolters do almost as much damage to their tanks as twin lascannons do, and they cost less than half as much. I'm assuming you don't have the parts for twin assault cannons, thugh those are the best guns hads down here, but sadly they dont come in the kit.

-Heavy weapons in tactical squads are not my favorite thing to see. If those are the only models you have, fine, but tactical squads work much better mostly focusing on special weapons, which they can shoot while they move to try and get into boltgun range. A plasma gun or flamer would probably do you much better in this situation than lascannons and missile launchers.

-If you were looking for something new to buy, as a previous poster said, Stalkers are amazing agianst all types of Eldar, Tau, and Necrons with their bonus to hit Flying things. But only if this was an opponent you would be playing aginst frequently would I advise buying something new.

-Dark Eldar have no defense against Psychic Powers at all. Swapping a Captain to a Librarian at this low of a points value would probably be a good move, and you could i n theory just use the same model to do so.

Now, as to tactics:

-Dark Eldar Raiders are going to be your first big targets to shoot down. Once they die, the major difference between kabalite warriors and space marines - 5+ armor and T3 instead of 3+ armor and T4 - starts to actually matter. If any of them have Disintegrators instead of Dark Lances, those are the targets to hit, 100%, they are anti-marine weapons that are very scary against primaris in particular.

-If he is (i assume) loaded up on blasters, and also has a number of Shredders, Splinter Cannons, and Splinter Rifles in his army, you want to make sure that everything in your army starts over 8" away from your deployment zone edge. You know with the low range of his weaponry, he will come to you, and your weaponry that has less than 24" range you care about much less than his. His vehicles move 14", plus an 18" range on his blasters and rapid-fire on his Splinter cannons means that his most important weapons have 32" threat. 24" is the no-mans land in normal deployment, and your most important weapons (heavy bolters, autocannons, primaris marine rifles, etc) all have 36" range. So on dawn of war deployment, start within 4" of the board edge. On hammer and anvil, within 16" of the board edge. Assume you will lose first turn, and you will find that you lose games because of it far less. Assuming that those squads are all 5-man with a special weapon in each, that means the difference between taking 40 poison shots and 6 dark lance shots turn 1, and taking 20 poison shots and 3 dark lance shots. That's the difference between 2 dead marines and chronus or the vendread at half HP, or 4 dead marines and one of those vital vehicles dead. On the flip side, assuming you get turn 1, it means you don't get to fire your regular boltguns at his tanks, but you do get to fire your flakk missile, your Hellfire shell (both of which will be hitting on 2s rerolling 1s thanks to the Signum on your devastators), 6 regular heavy bolters, 5 primaris bolt rifles, your sniper rifles, and your four autocannon shots at him, which is enough to knock down both Raiders with average rolls. the boltguns would barely make any difference.

-Anything that gets cracked out of a transport should be shot down with anti-infantry weaponry. tactical squads sitting in cover trading fire with kabalite warriors or wyches will win, and units like wyches are far easier to deal with before they crash your lines and start murdering you.

-The only units you really ahve to worry about in close combat are the wyches, the HQs, and the incubi. most of them (possible exception of the Archon before his shield gets blown) can be bounced by your own characters or dreadnought, and the succubus or the wyches could be punched by the primaris marines if you got the charge - if he gives you the chance, dont hesitate to charge because you're worried about the swing back. Primaris marines charging incubi kill 2 on the charge, or half-health the succubus/kill half the wyches. close combat is not totally hopeless for you. Thats not even thinking about the Reaver bikes or Kabalites, who you can easily take if given the chance.

Overall my advice is: dont get discouraged. Getting good at your army when your codex is among the worse ones in the game means when you do inevitably get buffed and your army goes up in power, you will be that much better at using your tools. Dont feel that changing your list is the only thing you can do to make a difference in your games - I promise it will only frustrate you more when it doesn't work.