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This is the paperback Kill Team supplement originally found in the Kill Team: Nachmund boxed set. Inside these 96 pages, you'll find full rules and background for both Voidscarred Corsairs and Chaos Space Marine Legionaries Kill Teams, datacards (including fillable blanks to copy), equipment lists, and Spec Ops rules including Rare Equipment.
Also contained within is a lore guide to the Nachmund Gauntlet, full killzone rules for using the terrain from Killzone: Nachmund, and the Shadow Operations: Nachmund Mission Pack.
You'll need a copy of Warhammer 40,000: Kill Team Core Book to make full use of this supplement.