Codex Alaitoc Eldar: Use the Auxilia Formation with Rangers from codex Eldar. However, instead of being able to take Rangers as non-Troops, they may be taken as transport choices for any unit that is allowed a falcon. When used as a transport choice, the unit ‘transported’ is guided by the rangers to their location, and therefore they are deployed within squad coherency of their accompanying ranger unit as if it was one unit with the Infiltrate ability. After deployment the rangers and their accompanying unit are split into their original units and are free to move and act as normal.
Codex Alpha Legion: Use Chaos Cultists as allies for Chaos Space Marines.
Codex Armoured Company: Use the Armoured Formation with Imperial Guard. The list generated is given as an example underneath the Armoured Formation rules.
Codex Biel-Tan Eldar: Use the Auxilia Formation with an aspect warrior squad (e.g. howling banshees) from codex Eldar.
Codex Genestealer Cult: Use Tyranids as allies for any army other than chaos daemons and necrons, but typically with Imperial Guard.
Codex Iron Warriors: Use Imperial Guard as allies for Chaos Space Marines.
Codex Iyanden Eldar: Use the Auxilia Formation with either wraithguard (to bypass the maximum squad size requirement) or wraithlords from codex Eldar.
Codex Kult of Speed: Use the Raiders Formation with codex Orks to generate the following:
HQ: Wazdakka Gutsmek, Warboss (warbike), Big Mek (warbike)
Elites: Nobz (warbikes or trukk), Meganobz (trukk)
Troops: Ork Boyz (trukk)
Fast Attack: Stormboyz, Warbuggies, Warbikers, Deffkoptas
Heavy Support: Any of the above.
Codex Night Lords: Use the Auxilia Formation with Chaos Raptors or Chaos Bikers from codex Chaos Space Marines.
Codex Saim-Hann Eldar: Use the Raiders Formation with codex Eldar to generate the following:
HQ: Autarch (wings/warp jump generator/jetbike), Farseer (jetbike) (warlocks on jetbikes), Baharroth
Elites: Striking Scorpions (wave serpent), Fire Dragons (wave serpent), Wraithguard (wave serpent), Howling Banshees (wave serpent)
Troops: Dire Avengers (wave serpent), Guardians (wave serpent), Guardian Jetbike Squadron
Fast Attack: Shining Spears, Warp Spiders, Swooping Hawks, Vyper Squadron
Heavy Support: Dark Reapers (wave serpent), Falcon, Fire Prism, Night Spinner
Alternatively, use the Auxilia Formation with the Vyper Squadron from codex Eldar.
Codex Ulthwé Strike Force: Use the Webway Strike Formation with codex Ulthwé Eldar to generate the following:
HQ: As normal
Elites: As normal
Troops: As normal
Fast Attack: Any unit
Heavy Support: Black Guardian Support Weapon Battery, Wraithlord
Although the above formation does not allow vehicles unlike the original Ulthwé Strike Force, the rules concerning webway portals have been changed since they were last mentioned in codex Eye of Terror. In codex Dark Eldar vehicles may not use a webway portal, but monstrous creatures can, so on the upside you can now have wraithlords.
Codex Word Bearers: Use Lost and the Damned or Chaos Daemons as allies for Chaos Space Marines, or Chaos Space Marines as allies for Lost and the Damned or Chaos Daemons depending on which army you want to form the bulk of the army.