So The Larkins asked me about what pitfalls a friend would hit getting into 40k with a CSM Thousand Sons army. I thought that I’d again poach answering the question to get an entire blog post, and further wanted to format my response according to some organizing principles. It kind of resembles a “Good News, Bad News,” but acknowledges that some challenges are of varied significance for different types of players.

Does Your Friend Like Converting?
This would also encompass a comfort level with conversion, of course. This matters for both overall aesthetics and specifically running the Rubric Marines (which are listed in the book as Thousand Sons). There is an upgrade kit available, though at 20 bucks for a handful of heads and other bits I’ve never been willing to put in cash for the similar Noise Marine one. If the friend’s comfy converting, though, he can probably get by just picking up dramatically cheaper boxes of Tomb Kings infantry and chopping and screwing that onto boxes of Chaos Marines (or even normal Marines, depending on what he wants).

Similarly, if he wants his non-Thousand Son marines to share an aesthetic he’ll probably want to be able to swap some bits and bobs in. I’d look at doing something similar to what I did with my Typhonic Beastmen, and just changing out the chainblades for the khopesh-style swords you get with Tomb King skeletons. That, again, does depend to some extent on how he’s playing his Marines; they come stock with pistol and bolter, and can swap the bolter for a melee weapon for free, or add the weapon atop the bolter for a pittance. So if he wants Marines that can run close combat it becomes an aesthetic consideration. There are build issues here too, in terms of army comp, but I’ll handle them in another section.

Does Your Friend Like Having His Entire Army in a Single Book?
Chaos Marines tend to struggle in single-book fashion. They technically have three books, because Black Crusade and Crimson Slaughter are both codices for the overall army, which tweak how you put the forces together. Neither of them really exclude running Thousand Sons, though both give you other options to meet your minimum troop choice allotment: Chosen—the Nobz of Chaos with heavy-weapon options thrown in; and Possessed, close combat Marines with better strength and Daemonic (including a 5++ invuln), respectively.

However, particularly right now when there are super-strange supply-chain issues and things trapped in resin, Chaos Marines struggle with cost issues if you’re playing them just out of the book. They have super cheap troops in cultists, but you can’t physically buy those in a super-cheap fashion right now. If your friend’s starting totally raw he could hop into the Dark Vengeance  box set; maybe you have another pall to talk into it, or he wants to reaaaally stretch his conversion and use the whole kit. That box gets you $40 of Cultists, which are otherwise only available in 5’s (and you can’t even run them in 5’s). That kit can then be supplemented with another box designed to bring you up to a full force.

However, I don’t run cultists, because for roughly twice the price in-game I can get a daemon who has the same and better stats, an always-on superior save, deep strike, and immunity to fear/running away/going prone. Cultists tend to need a babysitter to prevent those morale issues. Similarly, the Raptor assault marines do roughly the same thing I get with Chaos Furies (and I kitbash my furies to avoid buying them 5 at a time for crazy prices). That does mean I don’t have the option of dropping a backfield meltagun party, though.

Since the primary value of cultists is holding objectives, not their shooting or assault prowess, I’ve found daemons do a similar and superior job. Specifically I run a goodly number of Plaguebearers, who enjoy both a 5++ invulnerable save and a +2 to any cover save they might be enjoying, making them exceptionally difficult to shift off of an objective or out of terrain. They’re no slouches in melee, either; they’re slow, but poisoned and auto-glance vehicles on 6’s, so they can be a hardy combat threat. They also have Daemon of Nurgle, which grants defensive grenades, both giving them the only base shooting attack in the Daemon troop codex and depriving charging enemies of bonus attacks.

The popular opinion is that basic Chaos Marines are too expensive for what they do, particularly since they’re vulnerable to running from combat and shooting and don’t auto-recover from flight like Space Marines do. That’s what makes your choice of troop so critical, since building a basic book army requires at least 2 units of them. Daemons, as battle-brothers to Marines, can take their transports; so you can buy a couple cheap units of bolter Marines, give them both Rhinos, then load your Rhinos up with Daemon troops for a turn or two of shooting protection as they motor up the board.

But, that does require investing in two codices and two separate armies, and that’s a thing not everyone wants to do! See also the following, though:

Does Your Friend Like Psychic Powers?
Dude likes Tzeentch, so I assume he at least kind of does. I mean specifically in the context of how the Psychic phase plays in the current edition of 40k. If there’s a Warhammer Fantasy background, it plays out similarly to that system. At the start of your Psychic phase you roll a die, and both sides get that many points for casting spells, plus points equal to the combined level of all your psykers. This matters with Thousand Sons because that specific unit, the Thousand Sons unit, must take its unit champion with each unit of 4 other Thousand Sons. Chaos suffers the tax for having a unit leader, like lots of armies do, but Thousand Sons specifically pay considerably more because their unit leaders are all Psykers. They start at level 1, and for a higher price can jump to 2; the danger though is that you’re doing that on a model with only a single hit point. I’ll address the Thousand Sons unit itself in a separate deal, but if you’re playing them you’re probably going heavy on Psychic powers. That means taking Psykers as HQ choices (which you’ll probably want to do anyway, see below) and trying to find a way to use those powers.

One major gripe with how Chaos Marines involves how they generate their psychic powers. All characters with a Mark are required to generate at least one power from that God’s discipline, and the discipline of Tzeentch is widely reviled (though, looking at it, it seems alright; certainly better than what Daemons of Chaos get). The changes with 7th let most Psykers gain the Primaris (basic) power from a discipline if they choose all of their powers from that discipline, but Chaos Marines and Daemons modify that rule. They always have the Primaris from the discipline associated with their God, but since Chaos Marines still have to “generate” their power from the discipline that forces you to double-dip. So unless you’re going to spend the extra points to upgrade each Aspiring Sorcerer in your Thousand Sons unit to be a level 2, you’re going to be using a lot of the same powers. That’s perhaps a bit inside baseball, but it matters because it means you probably want additional sinks for your Psychic Phase; daemon summoning is a great one, since you’ll be generating lots of points, but that not only means you need daemon models, it means you probably want to consider at least a Daemon Prince. Casting the summoning powers as a non-daemon drastically increases the chances you’ll explode in a nasty fashion, and while Chaos Marines have some options to re-roll casts, an actual daemon is safer. The aforementioned Crimson Slaughter Codex offers an option whereby you can make one of your characters into a daemon, though he can then only join units of Possessed; this can provide a not-crazy-expensive workaround (since you get the Daemon invuln save and don’t need to buy your own), but it’s not a path everyone wants to take. Again, taking units from the Daemon codex also gives you a lot of psychic powers that you can burn points on, and the Tzeentch Daemon troop unit generates psychic charges on its own and is great for churning out summoning spells, since a warp explosion won’t kill every body in the unit unless things go real, real bad.

Does Your Friend Mind A Small Model-Count?
Not unlike Grey Knights, a full-bore, icons-to-the-wall-and-fused-there-with-warpflame Thousand Sons army is going to be very expensive. You’re paying almost double the cost of a standard Chaos Marine for each Thousand Son model you put on the board. That mandatory unit leader, the Aspiring Sorcerer, runs more than double that price. You do get a lot for these guys, though. Each one comes standard with an Aura of Dark Glory (5++ invulnerable save, boosted to four up  thanks to the mark) and Inferno Bolts (AP3! for your bolters). This means that Thousand Sons are resilient and good at cutting down enemy Marines, or at least forcing them to fall back on inferior cover saves to survive. The unit’s also Fearless, so no worries about running away, but it’s also Slow and Purposeful; that means you’re not only not running at any time, you don’t get to overwatch being charged. Since Thousand Sons aren’t great in close combat, that’s a concern. The unit also has Veterans of the Long War for Preferred Enemy (Loyalist Marine Scum) and a bonus to Leadership that’s irrelevant since they’re already maxed on that stat. Your Aspiring Sorcerer also gets a Force Weapon, which in the current edition gives him a 1-charge psychic power that grants him instant death on his melee attacks. Not a lot of attacks, but could scare some monsters away. The Thousand Sons can also take a special banner, but unlike the sexiest of those banners (units with the Mark of Slaanesh can get Feel No Pain from theirs) it only adds Soul Blaze to bolt fire from the unit; that’s some theoretical bonus wounds, but generally it won’t show you much.

So if he’s specifically into Thousand Sons…and he wants to actually, you know, take the Thousand Sons unit…it’s going to run him a fair price in army points. Mobility’ll also be a factor, and Thousand Sons don’t get the option of buying further heavy weapons (though you will always have that Psyker in the unit). You can build the unit as high as 20-strong, so you could run an implacable gunline; or you could keep them small and tight in Rhinos, but then you start really feeling that tax on each Aspiring Sorcerer.

One other thing that’s important to understand about the Thousand Sons unit is that you can take it as a troop so long as you A) have a Chaos Sorcerer marked Tzeentch and B) are taking Chaos Marines as your primary army. That second rule is archaic in the current way of things, which favor mixing armies and letting people take different forces as allies; the similar rule Daemons had regarding taking their Heralds was errata’d to drop the primary rule. The overall concept, though, is equally archaic these days, and likely to disappear/be replaced soon with Formations and Detachments that allow easier blending of forces. I’m guessing we’ll see some of that this coming weekend with the Khorne Daemonkin codex. The current way of things is for armies to just have a different Force Organization chart, such as the Ork one that offers more HQ slots but demands more Troops, or the other one that gives you more slots at the Elite level but requires certain purchases and special rules.

For the Chaos Marine codex, though, you just have the unlock option. Every other God lets you select their special troop when you take a Chaos Lord; only Tzeentch requires a Sorcerer. There is, again, that Tzeentch tax in that you’re going to have two powers from his Discipline, but a lvl 3 still has some room to run around in another valuable discipline like Telepathy (for defense) or Biomancy (for shooting). Pyromancy got dramatically better in this edition, but it’s not rolled on a ton. Taking this Sorc cuts a lot of cost out of your overall army, because now you’re not worrying about buying standard Marines or Cultists unless they serve a purpose; you can just fill your army with implacable, power-armored monster golems.

Does Your Friend Want Some Good News?
Because, you know, I could see that he might. Good news for a Thousand Sons/Tzeentch Chaos Marine army includes:

•  You get an invuln, and YOU get an invuln! The mark of Tzeentch itself gives a model a 6+ invulnerable save or improves any save it already has by 1. That’s why the Thousand Son troops are 3+/4++, and that does have value. You’ll shake off Marine-Killing fire more comfortably than comparable forces, but may still suffer due to low model counts. However, if you build your army using the Crimson Slaughter codex and take Possessed (which you can do anyway, but the Crimson Slaughter gives them a different mutation table with greater mobility in addition to making them troops), those Possessed enjoy the 4++ save if you mark them Tzeentch since they’re already Daemons. Warp Talons can also enjoy this. You could also go cheaper and just run a horde of cultists with a “Pray to the Dark Ones” save that makes them trickier to remove than they’d otherwise be.
• So much AP3. Thousand Sons units are capable of shredding marine targets, and the fact that they can move, shoot rapid fire weapons, and then charge afterward allows you to bring down the weakened units. It helps to have something to pull folks out of cover or punish their being in it, of course, and that leads to…
• Daemon Engines! The Daemon Engines are visually sexy beasts, including shooty and stabby 
• Obliterators and other 2+’s! I’d stay away from Mutilators until rules are granted to them that aren’t terrible, but Chaos does have access to the cheapest Terminators, plus Obliterators–Terminators at double+ the cost, with twice the wounds, a 5++ save, and an a la carte menu of heavy and special weapons. You can always buy much cheaper Havocs (Your heavy-weapon Chaos Marines), though they’re more fragile. You may want one unit armed with rocket launchers to deal with enemy fliers, of course; myself, I tend to rely on Soul Grinders from the Daemon codex.

This is all broad-brush, of course. Adding Daemons to the deal opens up a lot of options, and a lot of speed. If you’re open to a couple other Gods getting their fingers in your army pie, adding Nurgle Bikers and Nurgle Chaos Spawn provide brutally resilient forces that can speed across the table and tie up enemy shooting while other waves march into place. Daemon summoning also gives an option for objective-grabbing, chaff, and assaults that tie up shooting phases until you can get in a superior position. Thousand Sons make a beautiful army, especially if the conversion work is intensive, and Daemon Engines provide additional benefits in that front because you can tinker with all of the gorgeous Tomb King models for various ends (such as Bloodcrushers using these guys).

I think they’re a wonderfully thematic army, which is kind of the wargaming equivalent of forces having a “nice personality.” That’s certainly not something I shy away from playing, though, as my Slaanesh’s Lament demonstrates. If new things drop any time soon that give a bit of a boost to the forces they’d be even more competitive, but for sitting down at a table with friends and throwing dice, I say recite the Rubric!