Codex: Deathwatch will be available this Saturday, but you don't have to wait to see some of the special rules in it. The Warhammer Community site announced a sneak peak into the Deathwatch Primaris Killteams, and how those units gain the special rules of their combined members.
Since some players may find these mixed squads to be confusing at first, here is a breakdown with a tabletop demonstration on how to organize these squads and how the rules add up as various model types are added to the unit.
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