I am not normally one for Allies, but I tried something today that I can only call devestating.
Farsight w/Bodyguard (as many as you like, kitted out as you like)
SM Librarian with Gate of Infinity.
Now, this is expensive. However, with the interaction of Farsights Warlord Trait, and the effect of Gate of Infinity, you can now zoom around the table risk free, laying waste to anything in your path. With volleys of Missiles, Plasma bolts, Fusion Blasts and torrents of fire. Add Target Locks so you can use each weapon appropriately of course.
You cant assault, but you won't need to if you pull this off properly, and buy staying mobile and making full use of markerlight support and an Ethereals "Grace of the Zypher" if you are close enough, you can Land. Run and then still fire horrifically accurate shots.
It is evil, maybe. Does it work? Hells yes.
It gets better. Re rolling to hit on marker lights for one and shooting overwatch at full bs. I am debating on taking Eldar or Marine allies for the psyker powers. I'm leaning toward Eldar since a Farseer wouldn't be a bad ideal.
Farseer on a bike can keep up with crisis suits and would be really good with O'Shova and his body guard which with the right upgrades can deny cover and be twin linked.
Pathfinders I think would shine and fire dragons as always would be awesome. Other than those units I really wouldn't bother with anything else. I might do farseer on a bike with pathfinders and leave it at that.
Shadowsun+Fortuned Seer Council
Re-rollable 2+ cover saves, Infiltrate, and throwaway 3++ saves.
Plus pretty reliable Fusion Blasters for anti-tank, which is perhaps the only thing the Council doesn't have (thanks for that nerf, GW!).
Best,
-BT