Orbital FSS

As a disclaimer there is usually one or two t3 clearing classes chosen, so I tend to lean towards orbital FSS most of the time. With that out of the way, lets get into SI choices first. Sky is the Way Is for boosting Attack Weapons Team , which can make or break key moments in the game including healing allies if they can walk under the liberator for healing. Whiz Kid boosts your Joint Fires Observer AND your Call For Fire that you will level up later in the game. Whiz Kid Also boosts any explosive items you find, which pairs perfectly with M5 MAR and/or Explosive Charge if you happen to find these. MGL should be left for medics, but extra 40mm can absolutely be put to use to save your mana and Joint Fires Observer charges. During the early/mid game, you should be collecting Incendiary Grenade , Explosive Charge , Energy Cell , and a Kinetic Integrator if you can get your hands on one. All of these items are integral to manage your mana economy as you have noticed I left out Energetic since it's not needed if you can get Energy Cell or a Kinetic Integrator . It is never guaranteed that you will find these items in large enough quantities let alone other players taking them, but you should be able to loot one or two items listed above.

Now for the skill tree, you want to max out Joint Fires Observer first, as it will be your early game self defence. With Whiz Kid bonus, this will reliably 1 shot Risen at hard difficulty or lower, unreliably 1 shot them at insane depending on how close to the center of the blast they are. Nightmare+ you will need two Joint Fires Observer for Risen , so you should save orbital strikes for other targets. Explosive Charge and Joint Fires Observer pair perfectly together for killing Hunter , Pure Hunter , Lacerti , and other smaller t1s throughout the game, saving your Attack Weapons Team , Call For Fire , and Rail Gun for more important targets. Laser Designator FSS is a useful ability, but I wouldn't use it too often as 35 energy is a lot when you are not investing in Soldier Skills or taking Energetic . At level 4 you should get Attack Weapons Team , and level 5 improve Attack Weapons Team as this is going to be your hail mary that can make missions or revives a breeze.

Next tree to max out is Indirect Fire Support , as the Binoculars FSS , FCD Flare , and Rail Gun will be essential for supporting the team. Following this build you should get level 9 shortly before, or during either chapter 2 mission where the Hive appears. This means Rail Gun should be ready to 1 shot the hive for your team, making it far easier to survive until chapter 3. Last but not least, depending on personal preference either begin maxing out Call For Fire , or mix in some Soldier Skills levels for extra max mana, movespeed, and marksmanship/burst. As far as I recall, Whiz Kid boosts Call For Fire which lets you get away with not having to max out Call For Fire in my opinion as the extra 2 or 3 levels into Soldier Skills at the end is a nice quality of life bonus.