This is the section to read even if you skip the rest, because it prevents a mistake that is invisible when you make it.
Frenzied Host carries the HOST Unique Tag. A Unique Tag stops you taking two detachments that share it. So the natural next step, and the correct one, is to look down the menu for another HOST detachment.
There is one called Mercurial Host. And if you look further, both detachments also carry the Reconnaissance force disposition, which reads like confirmation.
Both signals are false. A Unique Tag is a printed property, not a word in a name. Mercurial Host carries no Unique Tag in Faction Pack v1.2, in Munitorum Field Manual v1.3, or on the community mirror. And a force disposition is not a Unique Tag: it describes what a detachment is for, not what it may be taken alongside, and unrelated detachments share dispositions all the time. In this faction, Rapid Evisceration and Spectacle of Slaughter both carry Disruption, and nobody thinks those are mutually exclusive.
So Frenzied Host plus Mercurial Host is legal, it costs exactly the 3 DP Strike Force budget, and it is a good army. It gets its own page.
In fact no Emperor's Children pairing is illegal at all, because this is the only detachment in the faction with a tag and there is nothing for it to collide with.
One thing we flag rather than hide. Faction Pack v1.2 states this tag in words. Munitorum Field Manual v1.3 lists no Unique Tag for any Emperor's Children detachment. Both documents are official. We tell you the tag exists, because the pack states it in words and because column geometry confirms the sentence sits in this detachment's own rules column rather than bleeding across from the stratagems, and we tell you it restricts nothing, because under either document no second detachment shares it. We assert nothing beyond that.