So, to be extra clear. In matched play, you cannot have a detachment bound by the CHAOS/IMPERIUM/etc. keyword, but you can have an army bound by the CHAOS/IMPERIUM/etc. keyword. Matched Play Examples: You cannot have a Patrol detachment of a WORLD EATERS Chaos Space Marines Chaos Lord and a unit of Plaugebearers, because Faction the only keyword they share is CHAOS. You can have a patrol detachment of a NURGLE Chaos Space Marines Chaos Lord and a unit of Plaugebearers, because they share the NURGLE Faction keyword. (This is a bad idea as you will get no detachment trait.) You can have a patrol detachment of a Chaos Space Marines Chaos Lord and a unit of Thousand Sons Rubric Marines, because they share the HERETIC ASTARTES Faction keyword. (This is a bad idea as you will get no detachment trait.) You can have an army consisting of a Patrol with a WORLD EATERS Chaos Space Marines Chaos Lord and a unit of WORLD EATERS Chaos Space Marines (they share the WORLD EATERS Faction keyword, among others), and a Patrol of a Chaos Daemons Lord of Change and a unit of Horrors (They share the TZEENTCH Faction keyword, among others), and all units within the army have the CHAOS Faction keyword. (Both detachments will qualify for their respective detachment traits.) You cannot have an army consisting of a Patrol with a WORLD EATERS Chaos Space Marines Chaos Lord and a unit of WORLD EATERS Chaos Space Marines, and a Patrol of a BLOODY ROSE Adepta Sororitas Canoness and a unit of BLOODY ROSE Battle Sisters. While the individual detachments themselves are legitimate, because there is no keyword that all units share (e.g. not all units have CHAOS or IMPERIUM), it is not a valid matched play army.
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