This buying guide was created by invitation by William Cruickshanks:

Hey there everybody. Jay's asked me to cook up a Buy List for the newest Warmachine faction, Infernals. I've played them extensively during the CID, and quite a lot afterwards too. I'll be talking through the fundamentals to get started with the faction, and then what I'd look out for when you want an eye towards competitive play.

Jay says the most common question is how many army boxes should I buy. My honest answer to this is probably one. Until you are getting near the stage of faction completion I don't think you particularly want duplicates of much in here. However, the Army Box is absolutely a fantastic deal and you should definitely get one of them, as it has a lot of what I would consider Infernal staples. Assuming we buy an army box we'll have the following models.

Zaateroth, The Weaver of Shadows
Griever Swarm (10)
Umbral Guardian
Lamenter
Cultist Band & Dark Sentinels (9)
Shrieker
Lord Adept Quintus Faustus CA
Desolator

Now, due to the way Infernals work you're going to have to invest quite heavily on battlegroup models for the faction to really tick. Summoning is the main and most powerful mechanic that Infernals have, and it's a lot less powerful if you don't have a swiss army knife worth of different tools to summon in. Here are the two lists I'd recommend building towards to get a good handle on the faction from the get go:

https://conflictchamber.com/?cg201b_-19o7oeocoaoaolonotomosoqoqoropogowovogoyogoh___-19o8oboeoaolonotomosoqoqoropofoyogovogoi

Infernal Army - 75 / 75 points
[Theme] Dark Legacy (CID)

!!! This army contains CID entries.
!!! This list is using a CID theme.

[Omodamos 1] Omodamos, The Black Gate [+28]
- Foreboder [4]
- Lamenter [7]
- Tormentor [12]
- Tormentor [12]
- Lord Roget d'Vyaros [4]
Great Princess Regna Gravnoy [0(6)]
Kezia Brand, The Screaming Night [4]
Master Theurgist Gideon Asher [5]
Mordecai, Master of Arms [5]
The Wretch [4]
The Wretch [4]
Umbral Guardian [0(6)]
Valin Hauke, The Fallen Knight [7]
Cultist Band (max) [7]
- Dark Sentinel (1) [2]
- Lord Adept Quintus Faustus [4]
Cultist Band (max) [7]
- Dark Sentinel (3) [0(6)]
Cultist Band (max) [7]
Griever Swarm (min) [8]

Infernal Army - 74 / 75 points
[Theme] Dark Legacy (CID)

!!! This army contains CID entries.
!!! This list is using a CID theme.

[Zaateroth 1] Zaateroth, The Weaver of Shadows [+26]
- Desolator [14]
- Foreboder [4]
- Tormentor [12]
- Lord Roget d'Vyaros [4]
Great Princess Regna Gravnoy [0(6)]
Kezia Brand, The Screaming Night [4]
Master Theurgist Gideon Asher [5]
Mordecai, Master of Arms [5]
The Wretch [4]
The Wretch [4]
Umbral Guardian [0(6)]
Valin Hauke, The Fallen Knight [7]
Cultist Band (min) [5]
- Dark Sentinel (3) [0(6)]
Cultist Band (max) [7]
- Lord Adept Quintus Faustus [4]
Cultist Band (max) [7]
Griever Swarm (max) [14]

Then after that I would recommend having a heavy horror stable numbering 3 Desolators & 3 Tormentors to get started with.

After purchasing the army box models you will need to buy are:

Tormentor *3
Desolator *2
Foreboder *2 (these come in packs of 2)
Cultist Band *2
Valin Hauke, The Fallen Knight
Wretches *2
Great Princess Regna Gravnoy
Kezia Brand, The Screaming Night
Master Theurgist Gideon Asher
Mordecai, Master of Arms
Lord Roget D'Vyaros

Infernals as a faction live and die by their solos, they're excellent and incredibly powerful models, so you will definitely want to pick these up to get started.

Looking to expand, a list of models I would recommend in a rough order of gravity would be:

Infernal Gate
The Hermit of Henge Hold
1-2 Soul Stalkers (these are the most niche heavy, but in a soul centric matchup can be gamechanging)
Agathon, Voice in the Darkness
Howlers
Expanding your existing collection of horrors. I would recommend a second Shrieker and then collecting a few more Tormentor/Desolators.

Once these are purchased you're basically good to go for competitive Infernals. Expanding the field allowance on your soulless units and some solos is basically all you have left to collect, barring Hearts of Darkness.

Speaking of Hearts of Darkness, I do not believe it is essential to play Infernals competitively and they have very much been balanced around Dark Legacy. If you have Hearts of Darkness lists you like the look of, or own models which you would like to play in the theme then that's fantastic. However Infernals as a faction are not balanced around relying on it for tournament play, so do not feel obligated to buy into this theme if you just want to play Infernals, that's absolutely okay too!