Hellow and welcome back to the webway!
With the idea of Footdar being quite viable due to the new Eldar codex. I was wondering if the army as a whole could benefit from the inclusion of Dark Eldar units. The reason why I suggested this is because I noticed that as a whole the Eldar codex lacks an efficient close combat unit. In addition, it appears that Footdar lists requires that alpha strike as well in order to prevent themselves from being wiped out.
With this in mind, I decided to look around for an unit that serves this purpose for the Eldar army, and I have found a few interesting ways in which units could be buffed. Now do note that I did not include the ideas of Venoms in the army, as I find that Venoms are best taken in units of 4 or more, and for blasters I find that you do not need blasters in a Footdar army. Lances maybe, but if you have only limited lance shots, then why bother?
There is also another reason why the baron is chosen; he helps you unlock other close combat options in the form of Hellions. They are troops due to the Baron and they do provide a mean punch that can be used to support the Warp Spiders as they rampaged on. I know that to use Hellions effectively, taking them in a large blob of 15-20 is a must and this could be annoying but think of it in this manner; Here I have an unit that can keep up with the Jetbikers, Warp Spiders and Farseers on Jetbikes and with the baron, they get stealth and other goodies and they can bash the brains out of most units without too much worry. It is a viable option that is underestimated.
This brings us to the other support for close combat units, I would say that taking in the Incubi and/or the beastmasters would be beneficial for Footdar. Incubi are essentially a mix between Scorpions and Banshees, and they complement both units beautifully and providing one of the few means for Eldar to counter Terminators in close combat. As for the beastmasters, the large ocean of beasts would also provide a very large and scary distraction that could take the pressure off the main Eldar detachment, and also provide a very formidable close combat element. The Baron can also sit with either units, depending on your choice and just be a happy sailor.
Of course, this brings us to the troop choices which must be filled. As I have stated before the Hellions is a viable option, but if the unit is not what you want then there are only two other options; Wyches and Kabalite Warriors. Wyches helps in the close combat department as well, and they are scoring troops. Combined this with Haywire grenades and you can have a very flexible unit that can help patch the weaknesses of Eldar. Kabalites Warriors could also be a solid troop choice for their capability to be a large blob of troops with poisoned shots that can deter many monstrous creatures from charging your lines.
Nonetheless, it must be noted that with every ally option, their inclusion is utterly dependent upon how they can synergize and also cover up the inherent weaknesses of the list. Doesthe parent list aims to spam as many guns as they could? Are they inherently mobile enough to not need counter-assault elements? This is also another issue of allying Dark Eldar units in a Footdar army, as some units may cause some inconsistencies in the way a Footdar list works. For example, if your army is comprised of Jetbikers in your foot list, then footslogging Incubi will be utterly foolish.
Another problem with Dark Eldar units in a footdar army is that quite a number of these units can actually be expensive, and sometimes you would want your allies to be cheap. For example the cost of a squad of wyches could cost about the same as two small squads of jetbikes or Rangers. Thus you will need to understand what you really want to do with the allied choice when you pick them for the job and how the cost justify the unit's role. In this capacity, I find that choosing Dark Eldar elements to support Eldar units needs to be a careful and deliberate choice, just as one would choose any unit in an Eldar codex.
In conclusion, I believe that Dark Eldar can be complimentary to the overall idea of Footdar, especially in the close combat department but one have to be careful not to dilute the list too much or you have a very weak list.