Editing Warhammer 40,000/9th Edition Tactics/Grey Knights (section)

===Allied Detachments===
With the entire army not being pure GK, the GK army loses Masters of the Warp, unless theyre AGENTS OF THE IMPERIUM (Inquisition or a superheavy aux of Knights)

====Space Marines====
Despite very similar appearances, GK are Santic Astartes with <brotherhood> and SM are Adeptus Astartes with <chapter>. By not being pure Adeptus Astartes the SM detachment will lose Combat Doctrines. Space Marine allies are varied and bring many things, depending on what your GK army needs.
*Special mention to Deathwatch, just because the normally pricey GK makes SM seem like the cheaper option, with Deathwatch, the GK feel like the cheap option...

====Inquisition====
While taking a single Inquisitor can be added to an existing detachment, as mentioned above, the Inquisition can also be fielded in entire detachment. This faction only has elites and HQ slots, so for allies, they need to be a Vanguard detachment. The main reasons to include Inquisition in a GK army are 2: they are cheap, and they have the "Authority of the Inquisition" which allows them to ride in your GK transports despite not being GK. So like your GK rhino with 5 Strike, 1 champion, 4 empty seats can fill those with inquisition.

====Astra Militarum====
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====Sisters of Battle====
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====Custodes====
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====Ad-Mech====
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====Imperial Knights====
*Of all your soup options, only Knights (well  and Inquisitors) dont break Tides. An advantage of having Knights is that they give you substantial board presence while youve got your heavy hitters in reserve. It's your choice of taking either one big Freeblade, or a hunting pack of 3 Armigers. 
**The Case For Armigers: Most other IMPERIUM factions would take the Armigers, because Warglaives are decently choppy and shooty, and having 3 of them can threaten anything. Helverins aren't bad either, because they're like Predators with an Invuln. A few Armigers and Dreadknights (if you aren't already using Armigers to proxy the fugly Dreadknights) can be surprisingly dangerous in large numbers  and you're honestly not spending that many points for what you get.
**The Case for a full-size Knight: You don't really have a ton of anti-Tank and long-ranged shooting that can survive being shot at like a Knight can, so having one is a useful distraction that keeps the pressure off your GMDK for a bit.