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.
Though their equipment is strikingly similar to Ruststalkers, there are a few divergent rules used by Infiltrators that provide a noticeable distinction between the kit siblings. With the titular alternate deployment method and the defensive benefit provided by Stealth, Infiltrators are certainly the more durable and mobile of the two units. Functionally the Stealth bonus makes little difference when the unit is out in the open due to already possessing 6+ invulnerable saves, but for the times when their 4+ armor saves are removed from the equation and those two Toughness 3 wounds aren't going to be saved by Feel No Pain alone, adding +1 to applicable cover saves can certainly be a difference-maker. Infiltrating gives the unit incredible flexibility during deployment in terms of restricting where enemy Infiltrators can be set-up, setting up early aggression or securing objective markers and thus potential victory points early in the match. Of course, exchanging both Transonic weaponry and Furious Charge for mere Power Swords or Taser Goads marks an obvious paradigm shift; whereas Ruststalkers are an unusual dedicated assault unit that is superior against elite targets, Infiltrators are more of a hybrid selection that doesn't particularly specialize in any kind of warfare. Their ranged weapons are low Strength but feature a high rate-of-fire making them ideal for hunting lightly armored non-vehicle foes, acting more in the roles of harassment and board control than anything else. Still, their Neurostatic Aura does give them some impressive support capabilities; enemy models within 6" of any Infiltrators suffer a crippling -1 penalty to their Weapon Skill, Ballistic Skill, Initiative and Leadership values. This combos exceptionally well with certain wargear options and the actual melee squads you can choose from (add Vanguard into the mix for more hilarity) though obviously close combat is not required to spread the love of deterioration with tight proximity being the only necessity.
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.
The Princeps for Sicarian Infiltrators is uniquely suited to a particular Relic of Mars, namely the Phase Taser; combining an Initiative test that runs the risk of removing the targeted foe from play with their Initiative penalizing Neurostatic Aura can lead to some hilarious assassination successes. Otherwise, the wide range of options available to a Princeps is handy but much of it will oft be unnecessary in many games, though Conversion Fields are nearly always worthwhile. Much alike to Ruststalkers, Infiltrators have two distinct wargear load-outs on a squad-wide basis that involve either Power Swords and Stubcarbines or Taser Goads and Flechette Blasters. The former is better suited for hunting medium to heavy infantry specifically what with the fewer AP3 attacks and higher Strength shots with an extended range, though generally I favor the latter variation for multiple reasons. The first of these is that Flechette Blasters are Pistols whereas Stubcarbines are not, meaning Infiltrators gain more attacks in close combat with the Taser Goads rather than the Power Swords. Secondly, the base Strength 4 of the unit itself means the trade-off between AP3 or +2 Strength with 6s on to-hit rolls generating additional automatic hits is slightly weighted against the Power Swords simply because of volume of high Strength attacks being more useful against a wider range of targets, specifically vehicles and even monstrous creatures. Lastly, five shots with Shred at Strength 2 isn't much of a downgrade in the ranged damage dealing department versus three Strength 4 shots - especially as both weapons lack an AP value - except against models either with high Toughness values or of the vehicular type. Ultimately, the Taser Goads are the better weapon in the context of the bonus attack for possessing a pistol in addition to a close combat weapon because of their versatility and the fact that they combine oh so well with any of the -1 Toughness effects that Skitarii can impose on their foes, inflicting Instant Death on what would normally be Toughness 4 models with multiple wounds.
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 are less of a dedicated assault squad than their kit-siblings by virtue of actually possessing ranged weaponry and lacking the Furious Charge special rule, Sicarian Infiltrators still primarily deal out the greatest percentage of their overall damage output in a melee. They follow many of the same principles as Ruststalkers; they are decidedly fragile for their cost and aren't necessarily the hardest hitting squad you could find but their unusual swiftness and added Doctrina Imperatives enable them to bulldoze most opposition provided you are tactful with their use. The mixture of Infiltrate and Dunestrider makes for one heck of a speedy unit that can put pressure on your opponent from the first turn onwards and act as a deceptively frightening distraction squad; players that underestimate them are often left with a decidedly baleful burn and those that don't will usually divert not insignificant resources into their destruction, a win-win for an advancing Skitarii force. Be sure to make ample use of their Stealth special rule and the fact that terrain is of little deterrence to them, keeping in mind that they do lack assault grenades and thus will suffer the full Initiative penalty for charging through cover - handily, Initiative 2 armies such as Necrons, Orks or Tau will still be made to fight simultaneously with the Infiltrators in such circumstances due to their Neurostatic Aura! If you have other vicious melee fighters in your force then consider teaming them up with the Infiltrators when faced with a particularly nasty threat as well as the Alpha level Doctrina Imperative to greatly amplify your chances of successfully neutralizing them. Don't be afraid to use the Infiltrators in a suicidal run by moving near a congested gun-line to crucially impose both the -1 Ballistic Skill and Leadership penalties on them, both reducing their outgoing damage-dealing capabilities and the chances of you forcing them to break from casualties sustained in the Shooting phase. Don't forget that these effects still work in combat as well which can easily turn a close victory in the Assault phase into an all-out rout of an enemy unit.
Thank you all for reading this article, I hope you enjoyed it! Sicarian Infiltrators are deceptive in their ability to win close quarters engagements and pressure the board because of their many various saving throws and additional deployment options, making them a powerful addition to any Skitarii force and one that your gaming partners will learn to respect either immediately or in due time. I'm eager to read your thoughts on these elite Skitarii forces and how your games have changed due to their presence. Thanks again!
We are all but a weapon in the right hand of the Emperor.
- Exhortationes Principiis Titannorum, Divisio Militaris