Perhaps the single greatest “OP” threat from the new Eldar codex is the ability to combine Wraithguard with D-Scythes (i.e Scytheguard) with allied Dark Eldar ICs and a WWP.
This combo enables deep striking from reserve with zero scatter, followed by hitting your opponent automatically with D-Scythes (since they are template weapons) — on a 3+, you then inflict D3 wounds or D3 hullpoints per Template, all at AP2, so no armor or cover saves (remember, templates ignore cover).
For most players, there is almost nothing you can do to stop this tactic, outside of using throwaway units to “bubble wrap” you important units and so prevent the Scytheguard from getting to them. Imperial forces, however, do have an option… his name is Inquisitor Coteaz.
Coteaz has been an exceptionally valuable HQ choice for several editions now, with his access to Divination, Ld 10 Stubborn, enhancement to Seize the Initiative rolls, decent combat ability, 2+ save, etc. What really makes him shine, though, is his signature “I’ve Been Expecting You” rule, which allows him and his unit to get an immediate free, out-of-sequence round of shooting at any enemy unit that arrives from Reserve within 12″ of him (and in his LOS)…. better yet, there is no limit on how many times this can be used and, unlike the Interceptor USR, it doesn’t preclude Coteaz and his unit from shooting on their shooting phase later in the turn.
So, how does this work against Syctheguard with WWP Dark Eldar deep-striking? Position Coteaz and very shooty unit in a central location with good LOS (the top of an Imperial Bastion works great, giving both a 4+ cover save and elevated LOS)… in essence, you then get a 24″ diameter circle in which the Scytheguard dropping in can get engaged and, hopefully, killed off before they get to shoot their D-strength templates. Have Coteaz cast Prescience on the his unit the turn before (if you expect enemy deep strikers) to make them even more accurate.
The very best unit to use for this tactic is, of course, Grav Cannon Centurions …. a 4 man Centurion squad like this, attached to Coteaz and with Prescience succesfully cast, with have 20 Grave shots, 17-18 hits, and 15-16 wounds, effectively wiping out even a 10 man Scytheguard squad and any attached ICs before they even get a chance to shoot.
Even if your opponent has multiple Scytheguard/WWP squads, Coteaz and Grav Centurions can take all of them down in a single turn, provided they land withing 12″.
Coteaz is not limited to Grav Centurions for htis tactic. He can attach to Sternguard with combi-weapons, a maxed out Henchman squad with Plasma Cannon Servitors and Joakeros (i.e. Lascannon/MM/Heavy Flamer choice each turn), IG Blob squads with multiple heavy/special weapons and TONs of lasgun shots, Long Fang squads with max Plasma Cannons, Vanguard Vets with dual-wiel pistols, Cult Mechanicus Kataphron Destroyers with Heavy Grav Cannons, etc. etc. As long as it is highly shooty unit with at least 12″ range weapons, it can combine quite well with Coteaz.
While this won’t solve all your Eldar problems, it goes a long way to stopping Scythguard (or any other WWP shenanigans) and can also counter all kinds of other deep strikers, like Eldar Falcons with Cloudburst rules, Space Marine Drop Pods, Tau Crises Suit teams, Chaos Daemons, and Terminators of all shapes and sizes.