|Death is my meat; terror my wine.|
I'm going to briefly cover some 6th Ed. rules that I want everyone to learn and utilize to their game. There's a lot of things that 6th Ed. brings that greatly favors Dark Eldar and I want to share them. Sure, there's some nerfs too, but I'd rather concentrate on the good stuff.
Night Fighting and Night Vision
Know that your entire army has Night Vision and that Night Fighting doesn't affect you at all. Also know that your enemies are in a world of shit if they're fighting Dark Eldar in the pitch dark. They literally cannot engage you if you're more than 36" away and this should effect how to deploy. Pre-measuring is in all the time now so you can deploy to best take advantage of these rules. If your opponents can only engage you by moving his vehicle 6", know that his threat range is then 42" away. Also understand that if you have Night Shields, the effective range of his weapon is also shortened, so you can pile all these on top of each other.
Another big deal about Night Fighting is that 24-36" makes you count as Shrouded, and 12-24" means you gain Stealth. Put this on top of the fact that you have 5+ to Jink and your Lances can negotiate enemy vehicles at 36" and gain 3+ cover save under Night Fighting if you move. This basically makes Dark Eldar the most effective army in the game when it comes to Alpha Striking with heavy weaponry under the Night Fighting rules. If you Turbo-boost your Raiders to get to a better location (say.. a distant corner that's near an objective), you will gain 2+ cover. If you find some nice cover for your Raider to shoot from, you can get up to a 2+ cover save from Night Fighting. That is huge. You must utilize the darkness to your advantage and that's one of the reasons I always take the Strategic Trait on my Warlord.
Cover Saves and Positioning
OK, not really right angles, but know that your vehicles are long and the front is narrow. This allows you to play very comfortably with the new cover system. 25% is incredibly easy to accomplish and you must use this to your advantage as well. There should never be a time your vehicles are not getting a 5+ cover from Jinking, or hugging 4+ covers from ruins and angling yourself from anti-tank weaponry so you get 3+ cover from it. You need to keep an open mind where your threats are on the battlefield and you must position your forces so you can bring down the full force of your firepower while leaving little to no options for your opponents to retaliate. Fast Skimmers can move 30" with the new rules, so you should always feel comfortable moving into advantageous positions on the battlefield.
I wrote an article a long time ago that still applies today. Don't be afraid to shoot things in cover if you know you'll get cover in return. Even though Dark Eldar can't trade blows with other targets, reduced cover saves (for him), Lance weaponry, AP2, Jink, Night Fighting, small unit profile, extreme angled shots, and Night Fields makes you a very difficult target to retaliate against. When played well, you should be able to outmaneuver and out-shoot even the deadliest of enemies. How this is accomplished is completely up to you. Just remember: If your opponents got a clear shot to one of your vehicles, you fucked up somewhere. This is probably the biggest thing that separates the good Dark Eldar players from the bad.
Directional Warfare and Focus Fire
The biggest change to 6th Ed. is the fact that the direction in which you engage your enemy (both ranged and in melee) means a world of difference. Keep in mind that one of the strongest strengths of Dark Eldar is that the army is incredibly fast. A lot of people take moving 12" and shooting for granted as DE, but in 6th Ed., it's so much more than that. Being able to draw the right angles so you can isolate and annihilate your enemy is king. You have to remember every time before you move, during your move and after you move, to look for the right targets. Some angles will remove the 25% cover, some angles will draw LoS to units out of cover, and some angles will put you closer to models with Plasma Guns/Meltaguns. The more you remind yourself to check for targets of opportunity, the more successful you will be as a Dark Eldar player. We are sly and cunning, and there's no greater display of arrogance than outsmarting our enemies on every turn. It's absolutely huge if you can pick off a Sergeant who strayed too far from his squad. I'm not even going to say how much of a game-changer it could be if you manage to drop a Librarian or USR-giving IC.
Focus Fire is what's going to make or break the Dark Eldar ranged game. I want you guys to read this section and memorize it until you can repeat the rules word for word to your opponent. I promise you, he will be asking for it after the things you do to him. Focus Fire is one of those rules I had to re-read multiple times because I couldn't believe how good it is. If you manage to catch your opponent's models out of cover, you can completely and utterly annihilate him before he has the chance to respond. Most of our units carry extremely powerful weaponry, with one of them sharing two magic numbers: S8 for Instant Death and AP2 for killing everything. On top of this, it has the Lance rule. Another thing about our army is that we don't pour out a million shots per turn and hope to get lucky, we put out lethal, precision-based firepower. Just think about it: If a Ravager can only put out 3 high-powered wounds per shooting phase, it makes perfect sense to look for a unit with 3 models out of cover if the opportunity presents itself. Focus Fire rewards a general's keen eye on the battlefield and punishes those not paying attention harshly.
Assaults and Challenges
Yes, we know that Overwatch is extremely damaging to our forces in assault. We must look at assaults from another angle; mainly the fact that we can now incorporate the benefits of Fleet with our ability to shoot. As you all should know by now, several of our units have access to Plasma Grenades. These grenades can now be used as a 8" weapon that drops a S4 AP4 Blast on your opponents before you charge in with the re-roll from Fleet. Never discount the grenade you have in your arsenal and the characters that carry it. Since our Archon and Succubus have extremely high BS ratings, sometimes its much more beneficial for them to throw a Plasma or Haywire nade instead of using their shot. However, this does not mean you should ever discount your ability to selective choose how to inflict wounds. If your Succubus is carrying a Blast Pistol and your Hekatrix has one as well, have a regular Wych throw the Plasma nade while the rest of your squad fires off Splinter Pistols. Once the wounds have been inflicted and the opposing player reveals his tasty Sergeant, let loose your S8 AP2 Blast Pistols wounds.
For me, this edition of 40K is a very heroic edition. Not only can your characters challenge, but they can make Precision Shots and Strikes. Whenever one of your characters rolls a 6 to hit in ranged or in close combat, you can choose which model takes that hit (hopefully from a Blast Pistol). This is huge because it allows you to pick out those models most dangerous to you. In close combat, you will always to challenge due to your speed and superior Weapon Skill. Challenges are extremely important to Dark Eldar because it allows you to bully squad leaders (such as Nobz and SM Sergeants) into submission. No one wants to lose that Power Klaw to a I6 Hekatrix with an Agonizer, but challenges makes it so he either has to risk losing it or not fight at all. This allows you to eliminate threats to your ICs and dispatch weaker characters with ease. No matter what, you get the chance to eliminate a high-threat weapon and hopefully drop the opposing squad's leadership as well. Challenges also keep your characters relatively safe because only one model is swinging into you. Keep in mind that challenges can also be used defensively to save the rest of your squad from danger. I can only imagine the rage in your opponent's hearts when you successfully tank Abaddon with a Hekatrix. It makes me glee.
There's a bunch of other small buffs lying around the 6th Ed book, but I think the ones listed above are the most important. Let's list them really quick:
Night Vision and Night Fighting
Cover saves, 25% cover and Jinking
Careful positioning, outplaying your opponents
Inflicting damage from selective positioning aka directional damage
Focus Fire and target priority
Shooting before you Fleet Charge; using grenades
Most of these are just 6th Ed. mechanics that you'll have to adapt quickly to be successful. Other aspects such as cover, careful positioning and outplaying your opponent will take more time. Out of all the armies in 40K, I view Dark Eldar as the most difficult army to play. This makes the victories so much sweeter.