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can my necron armie legally hire kroot mercenaries, they look cool, and i would like some cheap CC troops, but it doesn't seem like it would fit with the fluff.
I'm pretty sure they can't ruleswise. I know for a fact Kroot can't ally with Space Marines, Tyranids,or Witch Hunters, so I assume Necrons are excluded too. Fluff-wise it doesn't work at all.
You are correct, Necrons can not ally with Kroot Mercenaries. For referrence, go to the sticky post at the top of this forum, it has a link to our "Codex" on the GW website.
On the second page under the first paragraph is a list of armies excluded from using Kroot Mercenaries.