Capabilities - I feel the key to understanding where and when to apply a unit in any given situation is informed by knowing their full capabilities off by heart; here is a look at what this unit is capable of.
Billed as the elite melee force of the Skitarii legions, Sicarian Ruststalkers combine archaic technology with augmented physiology to cut deep into a freshly opened wound in the enemy force and sever it completely. However, they aren't ones to take a blow in return as ably as the veterans of other factions; each model has two wounds, a Toughness value of three and the Feel No Pain (5+) special rule. Their 4+ armor save makes them quite resistant to small arms fire albeit with the caveat that they can be wounded very easily by most attacks, though their 6+ invulnerable save and improved Feel No Pain roll make stripping each individual wound per model much more difficult than for regular Skitarii infantry. The actual problem lies in their high vulnerability to Instant Death or Strength 6 attacks that entirely negate their two wounds each and Feel No Pain, and many of those weapons similarly bypass the 4+ armor save or even any relevant cover save the Ruststalkers rely on - hence, the 6+ invulnerable save acts as a kind of last resort against problem opponents. Despite this, the Ruststalkers do have an outlet and that takes the form of the Dunestrider special rule; adding 3" to their Movement, Run and Charge distances, Ruststalkers are more than capable of closing the gap with foes in quick time - don't forget that most Skitarii detachments will benefit from Scout as well. Their complete lack of ranged weapons lends itself well to sprinting across the battlefield and making full use of that Dunestider rule; assuming no terrain makes its presence known, Sicarians of both types can move up to a whopping 18" across the full turn. They do suffer from lacking the Fearless or Stubborn special rules and as such can be aggravatingly Pinned or forced to flee - often a death sentence for a dedicated assault unit - but the various Leadership boosting items, their high base values of eight and nine on that front plus a particular Relic of Mars can all serve to alleviate that issue.
While their ranged presence is non-existent, Sicarian Ruststalkers truly make their presence felt in the Assault phase with a mix of incredible melee weapons backed by some handy special rules and supplementary wargear. Bearing deadly Transonic machinations, whichever configuration the Ruststalkers elect to utilize will deal armor-ignoring wounds on any six for a to-wound roll in the first round of a combat and then, as their strikes "adapt", they will then dish out a full-on AP2 offence that can scythe through the most heavily armored foes you come across. As such, Ruststalkers are your counter to enemy Terminator equivalents and even monstrous creatures as throughout the entire combat all those sixes on to-wound rolls will harm the target regardless of their respective Toughness value. Weapon Skill 4, Initiative 4 and a base Strength 4 might not lend itself well to dealing with high value targets but this is where the aforementioned outside bonuses come into play, namely the fact that Ruststalkers all have Furious Charge and can hugely benefit from any Conqueror Protocols activated with the Doctrina Imperatives - three attacks per model or four on the charge at the very least give them the weight of strikes needed to destroy their opposition. A full strength onslaught from a unit of Sicarian Ruststalkers backed by the Alpha level Conqueror Imperatives is truly terrifying to behold and especially so if they can get into a multiple turn tug of war where their Transonic weapons unleash their true devastating potential. What really drives this home are the units' unique Mindscrambler Grenades that give them the ability to ignore the Initiative penalty when charging through terrain, lob a Poisoned and Haywire small blast or cover a vehicle in multitudes of Haywire attacks to render any kind of armor useless against them courtesy of the accompanying Transonic weapons. They can tear anything from Tesseract Vaults to Cultists apart with impunity and this is what makes them a fragile yet undeniably highly damaging tool in the Skitarii arsenal of war.
How to Equip Them - Outfitting a unit is often even more difficult than determining the number that you employ, so having appropriate context for each choice is key; this rounds out the most optimal ways to equip a squad.
On a unit-wide basis the choice between the stock Transonic razor, Chordclaw and Mindscrambler Grenades or the paired Transonic blades seems rather difficult at first but I've actually found a rather simple solution to get the best selection. Both load-outs provide the users with the dual close combat weapon bonus, the former benefits from a single Fleshbane attack and the latter has +1 Strength on all of its attacks; in that context I would err in favor of the latter, but that is before one considers the far reaching effects of Mindscrambler Grenades. Acting both as Assault Grenades and Haywire Grenades, the minor advantage the Transonic Blades have against most targets is quickly lost out wherever vehicles or charging through cover are concerned - both of which should be fairly common occurrences in your matches. It becomes a question of raw damage output against models with a Toughness value - as well as the potential to inflict Instant Death on Toughness 3 models - versus always striking at full Initiative value on the charge to gain an obvious advantage wherever slower foes are concerned and also having far better general anti-tank capabilities. In most games, the latter is typically what you want to have because base Strength 4 is generally going to be enough against most foes, and that's not to mention that the Fleshbane attacks offered by Chordclaws will serve you so darned well with the increasingly common Gargantuan Creatures running around nowadays.
Contrary to the rest of the unit, the Princeps can still get the particular benefits of a Chordclaw alongside the paired Transonic Blades should you opt to field those, combining the higher Strength regular attacks with a single Fleshbane strike. Elsewhere, the Princeps has access to numerous options that can really change the make-up of the unit, though perhaps the "generic" one is the Prehensile Dataspike - granting a "free" Haywire attack at the users' base Strength that is always resolved at Initiative 10 is a fairly handy little add-on. Like Skitarii Alphas, a Princeps is capable of using Refractor Fields, Conversion Fields and Digital Weapons; I would actually vote in favor of the Conversion Field if you are looking for a defensive boost as Sicarians are universally Initiative 4 and thus much less likely to suffer from the Blind effects it offers, but I would skip Digital Weapons here as per the Skitarii Alphas. Of further note is the partially restricted access to Relics of Mars for a Sicarian Ruststalker Princeps - he or she cannot use the Phosphoenix - but any of the available choices are generally more powerful here than for other Skitarii characters due to the mix of Furious Charge and their already volatile melee attacks; I would probably leave Arkhan's Divinator to an Alpha and focus more on the close combat boosters.
Best Uses - It is true that each unit in the game ultimately has one or a handful of tasks they are best suited for in a general sense; these are the most efficient uses of this unit based on their capabilities.
Though they lack the Infiltrate special rule as per their like-named kit siblings, Ruststalkers can nonetheless cross the length of the board ridiculously quickly with the Dunestrider special rule. Add on the fact that most Skitarii detachments confer Scout on all their constituents and you can cease to worry about the mobility of this particular dedicated assault unit. Feeding into this and seeing as the vast majority of high Strength attacks in a standard match will come from ranged weapons depending on the foe you face, it only makes sense that you should try to get into combat as quickly as possible - in theory anyway. Provided they are armed with Mindscrambler Grenades there is little that your Ruststalkers can't legitimately threaten so you have a lot to work with in regards to effective targets, whether it be Super Heavy Vehicles or 2+ armored elites. There are many things to be aware of when attempting to get the most out of Ruststalkers; you need to be constantly aware of any Strength 6 or greater weaponry on the battlefield and try to hide from them or otherwise limit the damage they can deal while your units advance.
Additionally, cover is a necessary evil to employ because a 6+ invulnerable save is not really going to save your Ruststalkers from armor-ignoring weaponry and, as I've alluded to above, Feel No Pain can't be counted on in all situations due to Instant Death. Ensure that you make full use of line-of-sight blocking terrain and even consider playing the waiting game by hiding around until a target presents itself by moving into close proximity of the hungry Ruststalkers; they can't really take too many hits themselves and their lethal damage output is very much based around prolonged combats. Basically, the standard tactics involving fodder assault units don't really apply here as Ruststalkers are simply too fragile, costly and often suffer from a numerical disadvantage; they are not a bludgeon but rather a scalpel, brittle and precise. The lack of ranged weapons - save for a single hurled Mindscrambler Grenade per Shooting phase - means that you have little choice but to focus all your efforts on either holding objectives, locking down an area by forcing opponents to come to the Ruststalkers and engage them or simply charging whatever gets too close for comfort. Players have learned to fear these units because of how surprisingly swift they can be as well as their deceptive damage-dealing capabilities, so be sure to keep that in mind whenever you wish to move or charge them.
Thank you all for reading this article, I hope you enjoyed it! I'm a big fan of Sicarian Ruststalkers but I can't deny that they have some serious issues that need to be worked out if you want to play with them, namely that the now "standard" Troops choice of the Eldar codex will pitilessly tear them to shreds regardless of cover or other contributing factors. Still, if you stick to them and start learning to analyze the situation on a turn-by-turn basis on where to apply their talents they can quickly become the stars of your matches. I would like to read your thoughts on the Sicarian Ruststalkers and how they have performed in your games - good or bad - as they are definitely a more "advanced" choice for a Skitarii player. Thanks again!
Fear the iron fist, for its grip is death.
- Ferromort of the Ordo Sinister Titan Legion