Sheskiin in all of her profiles brings a BS 15 and CC 24 meaning she is good in any sort of engagement. Her equipment also includes a Pulzar direct template weapon, D-Charges, and a Double Action CCW. She can be armed with a Multi Rifle, or a Red Fury at no Special Weapon Cost. No Wound Incapacitation and Fireteam: Core means that she can be very deadly at range, and this is her primary role. In Close Combat she has access to the Protherion level 3 skill. This gives her access to bonuses similar to Martial Arts and more importantly allows her to steal up to two wounds inflicted in CC gaining them as additional "power up" wounds.
Due to this the Red Fury is a difficult choice for her, because even though it is patently superior to the Multi Rifle, it has Shock ammunition and will leave less enemies for her to consume.
You do not have to run Sheskiin in a Fireteam, and indeed most of the Shasvastii Fireteam options are very expensive, but she does excel with the additional burst and BS.
Sheskiin has basic armor and BTS stats, but her high BS and PH stats are likely to help her stay alive. She also has access to two defensive tricks: Nanoscreen and Valor: No Wound Incapacitation (NWI for short)
Nanoscreen means that she always counts as being partial cover against BS attacks. This will not help against templates of any kind, but most of the time you don't have to worry about running from cover to cover and can instead put her in the best spot for range and future movement. Remember that fire attacks will burn off your Nanoscreen be sure to scope out the enemies weapons for flamers or rocket launchers before putting her to use.
NWI will also give her a valuable additional wound against non-shock weapons. She also has Kinamatica 2 allowing her a little more movement when dodging. Given her expense, and lack of Visor, it can be worth while to put her in a 4+ member fireteam to give her access to Sixth-Sense level 2 so that she is not picked off by Camo troopers or shot through smoke.
Sheskiin has Protheion allowing her to eat enemy models for more wounds or to recover her lost wound. It is worth the extra investment of orders to get her powered up so that she can begin to use her offensive stats with less risk of losing her.
As with most high risk high reward models it is best if you can leave her in reserve to use once she is power up, or sacrifice her to gain an insurmountable damage. This unit can be considered one that required more training and skill to use well, but which has capabilities that make it very deadly in the right hands.
Sheskiin also has access to the Free Agent skill which allows her to switch between combat groups. Because of this it can be worth buying her as the one expensive unit in a higher order count list and swapping her between combat groups as needed.
Before she powers up Sheskiin is vulnerable to shock ammunition. Mines are particularly worth while because while she can dodge them, she will do so at 12s with a high likelihood of death if she fails.
If Sheskiin is in a link, don't try to face her head on. Instead drop a few members of the link team. Even if you only remove one member you significantly reduce her effectiveness and backup link members are unlikely in the Shasvastii sectorial. Once you have reduced her to a three or less member Fireteam, she becomes very vulnerable to TO camo or ODD models who can blunt her amazing BS and force her to dodge instead.
Sheskiin is a glass cannon, and if you can stack modifiers against her, she will go down soon enough.
Because of her expense Sheskiin is not really a "drop in" choice. She needs support to get things done, so will likely be the focus of any list she is brought in. In the Shasvastii sectorial this is even more true since she has access to a Fireteam. You will need to decide if she is best with a team of Gwailos (more offensive) or Calibans (more specialist options) is best for her. Remember that she can also link with Corax Hasht (the Shasvastii character spec-ops) which means that a single Gwailo or Caliban can accompany them for an expensive but small team.
Another novel option is to place her with several Gwailo Rocket Launchers using the Gwailo's for early game ARO and (a likely smaller) link for Sheskiin later game.
Keep her safe. If you are not going first your opponent will look to kill Sheskiin before she gets powered up. If you are going first, be wary of opponent traps or taking too many or two high quality AROs early. You should look to put her somewhere that allows her to get to mid field as quickly and safely as possible so that she can start putting her superior stats to use in a good range band. Watch out for mines!
Active Turn Role
Sheskiin's job is to kill as much as she can, and eat as much as she can. In a Fireteam she will look to push up on weaker enemy models destroying the order pool rather than going toe to toe with the enemy heavy hitters. If you brought the Red Fury version, this may mean letting other models put enemy into unconscious state or cover them in smoke templates so that she has something to eat. Once powered up, she can look to destroy enemy heavy hitters, but her weapon options mean that outside of CC she is unlikely to be useful against anything as heavy as a TAG.
If you do get a change to get her into melee with a high armor model TAG or HI though, don't forget about D-charges which can be used at a -3 and may be necessary. Only do this on ARM 5+ models though, otherwise the higher chance to crit is simply better.
With a Multi Rifle and in a Fire team Sheskiin can be a dangerous ARO, but most of the time she is going to want to be far from the enemy at the end of her active turn. She is very fragile, so don't hesitate to Dodge to a safer area if it is the same or better odds than shooting.