Rubric Terminators. Rubric. Terminators. Have you ever read the Horus Heresy novels and noticed that the Thousand Sons had these sweet ass, psychic, foreshadowingly stoic Scarab Occult Terminators that were literally described as "automatons" and "like robots" by Jaghatai Khan and Ferrus Manus (although the latter was most likely a compliment)? Did you ever wonder what happened to them? Apparently, the Thousand Sons still had them all this time, but Magnus had stuck them into the bottom of the pantry to save them for a rainy day. War Zone Fenris was that rainy day.
Why did they get Rubric'd?
You may have noticed the Scarab Occult was originally composed of the legion's best and most disciplined psykers. So, if Ahriman's Rubric transformed astartes who had little to no psychic abilities into dusty power armors, why did most of the Scarab Occult also get the Rubric treatment? Because the Rubric was retconed into affecting everyone but the most powerful psykers. Meaning that only a few of these guys managed to power through it, while the rest turned to dust because they just weren't powerful enough. That and Tzeentch likes ambition. These guys were automatons in all but name, who loyally served Magnus and...that's it really. Tzeentch no likey.
On The Tabletop
While the anti-Rubric Marines group are probably groaning at the moment, they're actually pretty good. You'd probably expect the 2+/4++ saves, Fearless, and AP3 combi-bolters, what you weren't expecting was the lack of Slow and Purposeful, one of Rubric Marines' chief weaknesses just gone and resulting in the odd scenario of Tactical Dreadnought armoured Marines being faster than regular Power Armoured Marines. You probably weren't expecting the Aspiring Sorcerer to keep the good stuff and be upgraded to ML2 (which means the option to roll a power on a second psychic discipline), and 2 wounds. They also have weapons options for a shorter-ranged Hellfyre Missile Rack that shoots kraks, and AP3 Heavy Warpflamer, or that odd Soulreaper Cannon mentioned above.
However, they still share in the Rubric Marines other traditional weaknesses. No combi-weapons and no AP2 power weapons means that they're still anti-MEQ specialists with limited options for countering cover, TEQs, and walkers. And with a minimum of 5 guys, the're still not a cheap option. The lack of options to negate cover saves is a particular issue as the targets you'd want to use them against the most; MEQs and Necrons, are almost certainly going to have cover saves (and inferno bolts do nothing about RP rolls or the FNP of Slaaneshi, Nurglite, Iron Warriors, and Iron Hands marines or the added toughness of Nurglites) and they are very pricey for the rather mediocre firepower per model they bring to the table. The AP3 heavy warpflamer is nice for roasting cover camping marines but it will require deep striking them to point blank range to get the most use out of and you still have to pay for the other terminators. However with two wounds they're pretty good at soaking up large volumes of fire thanks to their Scarab Occult Armour; requiring an average of 38-39 lasgun shots to kill and with their invulnerable saves and their two wounds they can tank plasma fire decently well; requiring roughly eight shots from guardsmen to kill and if you can get Endurance on them from some source they can be amazingly resilient to the point of nigh invulnerability. In conclusion their firepower is overall quite mediocre but their durability is top class among TEQs; though against the likes of meltaguns and lascannons they aren't anymore resilient than any other T4 model with a 4++ save.
For some reason even though the Forge World 30k line shows them in Cataphractii, in 40k they're in Tartaros.
Scarabs are probably one of the best-improved(if not the best) units in the codex. They wield magic versions of Loyalist Terminator weapons, and they're now led by a fully-fledged Psyker. Compared to previous editions, all your Aspiring Sorcerer now act like the nerds they're supposed to be, able to cast the same D3/D6 Smite as everyone else, and still know at least 2 other spells beyond that. The codex also gives them many ways to make them Your Dudes by inducting them into a secret, special clubhouse, spending points for Legion Command Upgrades or even spend a CP to give them a pimped out staff. For example, by inducting them into the cult of time and spending +15 points for Rites of Coalescence, you can restore a model back to full-wounds each Command Phase AND bring one model back from the dead in the Psychic phase, which makes them insanely durable as they are now 3W a model and Obsec. If you really want to out-endure Death Guard, for 1/3 CP you can steal their 9E Disgustingly Resilient Rule and subtract 1 from damage, which is supposed to help you trigger All is Dust
T4 3W, 2+/5++, 1+ Armour against D1 weapons, but All is Dust unfortunately only applies to Armour Saves now so no more 4++ Invulns against other bolters. Inferno combibolters are still RF2 S4 AP-2 D1, but you're a terminator so you're always shooting all four shots. The virgin Power Swords of 8E are now the Chad Prosperine Khopesh, which is S+1 AP-3 D2, which means they can do ok in melee against other marines (Interestingly, Grey Knight force weapons are now a flat D2 as well, so it could be that your Scarabs still retain enough of their powers to channel into their weapons, but your sorcerers must take the super swingy S+3 AP-1 Dd3 Force Staves unless you give up bolter to take a sword, too)
One in 5 (2 in 10) can replace the combi with a heavy weapon, and move and fire without penalty. Your options are: Hellfyre Missile Racks, which are Heavy 2 Krak missiles, and the same model can also take a Heavy Warpflamer (Heavy Flamer with -2 AP, pass because 4 warpflamers on cheaper rubrics is always better) or a Soulreaper cannon (Heavy 5 S6 AP-3 D1)
- Terminators can teleport around the field with the Cult of Duplicity. As falling Back now stops you from casting, and redeploy abilities are specifically NOT falling back nor coming out from reserves, you are much more mobile in this cult than in others, still able to shoot,charge, or cast to contest objectives.
- You are not the best in combat, but you can definitely bully those who aren't built for it/have Damage 1 weapons. Shred TROOPS with AP-2, but leave enough of them to charge and challenge those objectives. Even Intercessors will get chopped up with 3A D2 Khopeshes, and if they survive, unless they're rocking PFs or thunder hammers, they're punching you at 1+, so you only get wounded if you fuck up and roll a 1.
- A full squad, fully kitted out and given Rites of Coalescence will set you back 430-450 points. One big model of ten would see the most use from Rites of Coalescence and Cult of time. For 1 CP, you can also use them as shields for your Daemon Princes, making them unable to be targeted, ignoring positioning rules, number of models, or Look Out Sir! so long as you're within 3".
- But splitting them in two is VERY helpful, partly for Cabal points and the additional sorcerer, but also since the best stratagems in 9e cost a lot more for 6+ models than for just one.