As many players search for new combos of DE + Eldar with the recent release of Codex: Eldar, I think one of the better combinations may be Incubi tagged teamed with a Spirit Seer.
Spirit Seer provides improved DtW for the unit against enemy psykers and pretty much all of his powers are quite useful to Incubi:
-Conceal --- Great Primaris that makes foot-slogging Incubi much more survivable
-Destructor --- Gives the unit some pre-assualt shooting "punch"
-Embolden --- Not necessary, but certainly keeps the Incubi in the fight when you really need them to hold
-Enhance ---- Incubi already have strong WS/I, but this can give them the jump on even enemy commanders/ICs
-Protect --- One of the best, turns the Incubi into "Terminators-lite" minus the Invul save, of course
-Quicken --- Great for making those Footslogging Incubi get around the battlefield significantly faster
-Empower --- Along with Protect, one of the top.... hitting and wounding MEQs on a 3+ while striking before them and ignoring power armor is brutal against any troops with Space Marine stats or below.
The only major problem is that the Spirit Seer can't ride with the Incubi in a Raider/Venom, which would have been ideal, forcing the unit to move on foot. That said, I think they synergize quite well, especially if the Spirit Seer is an ally, since now he unlocks Wraithguard/Wraithblades as allied Troop options (who can ride in the outstanding Wave Serpent, by the way), greatly buffing a DE primary detachment.
