The signature rules differentiating harbingers from archai aren't great, but the general morghast rules are alright imo, at least since their points came down in the last battle scroll. Compared to stalkers at the same points they effectively give up some durability (-3 wounds per batch) and some hitting power (equivalent to -3 attacks with precision aspect) in exchange for 2" reach, +4" move, flight, and an aura that completely blocks out enemy command abilities. Both stalkers and Morghasts can be battleline fairly easily. At first the tradeoff of damage and durability for maneuverability and anti-CA tech looks reasonable, especially with how effective anti-CA tech is against OBR and how common the mirror match is these days. To me what tips the scales against Morghasts when compared to Stalkers and immortis is that mortarchs and boneshapers can return slain stalkers and immortis to their units, albeit unreliably, while they can only heal injured morghasts, they can't return slain ones to the board.
Since their points decrease it wouldn't take much to tip that scale, though. We're expecting more OBR nerfs in the next battlescroll, possibly as soon as September, since their competitive win rate still remains well above the target threshhold despite the previous nerfs. I wouldn't be shocked to see points increases for both immortis and stalkers, possibly up to as much as 240 per batch for each. If Morghasts remain at 220, or even go down from there, then we might start seeing them.
Though with further nerfs and points increases in the faction we might see less of OBR altogether. Then again, I was pessimistic after the previous battlescroll, and that proved wholly unfounded as the bonereapers kept right on steamrolling Andtor like nothing ever happened, so my predictions should absolutely be taken with an extra helping of salt.
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As for the prospect of a morghast hero, that's far from confirmed. The picture certainly looks like a morghast wing, but it could be a lot of things, and even if it is a morghast it might just be new models for the existing morghasts, or a new morghast unit that obsoletes rather than buffing the existing versions. If it is a Morghast hero that might encourages fielding them if it supports or buffs the existing units, but if it's just an individual tough fighty guy with the anti-CA aura then it would likely end up being an alternative to the existing morghast units rather than something you run with them. Even in the best case scenario - a morghast hero that is worth running on its own BUT ALSO makes other morghast units better, I'm still not sure how much of a competitive impact it would make at the moment. After all, a morghast hero is relatively unlikely to be an Andtoran Locus, as it probably wouldn't be a spellcaster, and even if it were it might have too many wounds. As long as the current season lasts, competitive OBR lists are unlikely to run heroes that aren't Katakros, Arkhan, or Locuses.
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But that's neither here nor there as far as I'm concerned. GHB seasons don't last forever, and we're likely less than a year away from 4th edition, so I'm not too worried about rules and points and balance and such. My interest in a morghast hero has always been more aesthetic. It would look cool, it would add cool new variety to our hero lineup, it's just a neat idea.