Forum adverts like this one are shown to any user who is not logged in. Join us by filling out a tiny 3 field form and you will get your own, free, dakka user account which gives a good range of benefits to you: No adverts like this in the forums anymore. Times and dates in your local timezone. Full tracking of what you have read so you can skip to your first unread post, easily see what has changed since you last logged in, and easily see what is new at a glance. Email notifications for threads you want to watch closely. Being a part of the oldest wargaming community on the net. If you are already a member then feel free to login now.

I just bought the Start Collecting! Malignants box as a base for my first venture into AoS. My local group is running 750 point games for an escalation league. I'm trying to figure out how to field this army in matched play. The Formation that comes in the box allow for 1 Mortis Engine, 1 unit of Hexwraiths, and 1 Spirit Host unit. On it's own, this is 460 of the 750 points. I can expand the Spirit Host unit to 6 models and add in 2 Banshees to get my to 740 points. However I'm not sure this army is legal.

Everything in the Army has the Malignants keyword, but that's not an actual subfaction. Everything but the Mortis Engine has the Nighthaunt Keyword. My guess would be that this would be a Nighthaunt army, with 2 leaders and 2 battline units, with the Mortis Engine allied in. But I wanted to make sure this was legal to play this way.

Unfortunately, by the book, Deathmages can't ally with Nighthaunts, which, in my opinion, is ridicolous and really stupid. I would propose your local group to allow you to expand the allegiance to Deathmages as well, as:

1) You're not exploiting any loophole or cheating to create an unstoppable army.

2) You are playing what was in the box before the whole allegiance thing.

Another slution could be to assembly the mortis engine as a throne of the coven, if you got the sprues, as it would have the Soulblight keyword. Still, that'd make it cost 260 points, and put it out of commission till you get to 2000 points.
As I said, your best option is to politely ask to let you inclde it as an additional alliance, since it'd fit the theme. I mean, you're not playing dwarves allied with dark elves and sylvaneths on the side...

it's odd that Deathmages and Nighthaunt cannot ally, since all of Nighthaunt and the Mortis Engine also have the Malignants keyword

Yes, it's indeed an oddity. I referenced the General Handbook 2017, and it states so. Malignant isn't a faction in the book, but I think nobody would object to your request of playing them together and benefit from the nighthaunt allegiance abilities.

I would let you do it, for what is worth.

None of the battalions in the Start Collecting boxes are meant for matched play. This one is no different.