As makes sense from his old name as Arkham Knight (Sniper), he is a shooting model mainly. His Combined Sniper Guns MKII are probably the best ranged attack on any Leader rank in the game, what with being Medium Range and Scope at triple blood, but they only have 2 ammo and Aim hinders his movement without another quite large investment in counters for Vanish. Rapid Fire is very good for him to use and should pretty much always be used, bumping him up to a better Assault Rifle in his 16" range, but at the same time he is relying on basic hit rolls with this gun and has nothing to boost it, so is still most reliable at nuking henchmen and other models with lower defence stats (or things near the Drone), because if he misses shots he's suffering a lot.
His EM Smoke Grenade is a great control option like most Smoke Grenades, but with the added benefit of having Light, single stun damage wounding on 3s (as opposed to none) and Electric for potential crit:Stuns. It also gives him the massively useful Vanish as a trait, which while costing him 2 counters it acts as an effective Mixed Combat Style, letting him shoot his EM Smoke with making an automatic hit, and if he is inside the template he can immediately be placed within 4". AK ignores the effects of the Smoke, and his place does not count as movement (thus not affecting Aim and letting him shoot afterwards) but does cost an ammo on the Smoke. Everything considered, it's a very useful trait to have that lets him cover himself with Smoke in awkward positions, but also to relocate and get into good shooting positions himself.
He does benefit from getting Reinforced Gloves care of Cybernetic Arms, but with no bonuses to his melee it is really just an option to have rather than a different playstyle.
Arkham Knight is deceptively survivable, as Defence 4 Martial Artist isn't amazing but he stacks a lot of other things onto it to help out. Endurance 7 with Kevlar Vest means he's taking a lot of hits before he does go down, and ignoring damage on those hits, while being an Acrobat at movement 4 means he can pretty reliably dodge enemy shots. His EM Smoke is also useful in this regard as it still behaves like a normal smoke grenade, and can help block off lines of sight or Blind an enemy beater. Agile is a little bonus that helps if he ever takes fall damage (and for someone who likes rooftops so much, it's possible) making him take an agility test and if passed, all fall damage is cancelled. There is a 66% chance of success on this, making him pretty happy to sit on rooftops where he can shoot below.
Most of Arkham Knight's kit is based around his combat prowess, with little left to note otherwise. He does have Undercover, which on him is mainly used to get into a good spot to ideally get a shot off turn 1, or to quickly reposition into somewhere he can be shooting from turn 2.
Another trait he has that's worth mentioning is Elite Boss:Militia Brute, which is ok but ultimately doesn't mean much as I will cover below with the Brutes themselves.
Scarecrow's offensive potential isn't in the form of pure damage. He is a control based leader, and this is what he does best by far. Inspire Fear gives him an action to choose a single model to make a willpower roll compared to the Inspire Fear chart as seen below, while he can use Discourage to penalise an opponent even more for this roll at the cost of all his SC (4 total). At a range of 4" it's something he needs to be careful with, although his equipment Secret Laboratory shores this up a little bit as I will discuss later. He also has a 1SC trait The Fear Master which lets him affect all non-vehicle models in 4" when he uses Inspire Fear, friend or foe (including himself) as well as giving it the Gas trait. This means any of the Militia henchmen who come stock with Gas Mask completely ignore this (as does Scarecrow, or anyone who buys a Gas Mask) but simply being able to hit everyone in a 4" bubble is huge, and can cripple a crew.
Outside of his defensive stats Scarecrow isn't all that impressive on the survivability front. Defence 4 and endurance 7 is pretty good for his points, but he has nothing that particularly boosts him up other than Psycho, which stops him losing willpower by any means.
Like all other Militia Boss options, Scarecrow has Undercover to both deploy further forward and reactively, being able to adjust to the opponent's crew (mostly). He also has Scientific, which adds 1 to his Special stat and makes him give away an extra VP on death (something quite nice on him though, and the old Secret Lab gave it anyway). Gas Mask keeps him safe from his own gases, but also many Ivy and Joker tricks, and Psychologist gives him a nice easy bonus on Riddles (auto 2VP, no roll) and a sub-trait to remove Mental Disorder traits temporarily. There aren't many models he has access to that have detrimental Mental Disorders though (Enchantress and Red Death are the only ones in Standard, although he can use it on enemies to remove beneficial ones).
Scheming:1 is ok, but really it won't mean all that much often because it is only a single model and you can just plan for it anyway.
Having attack 4 is pretty great, especially when his weapons are added in. With Handy to reroll hits he is fairly consistent, and Reach giving him extra range on his attacks (somewhat making up for his slow movement) he also wounds on 3+ with double stun, making him a pretty great KO piece. With +1 to hit from the Drone he is a veritable monster.
His strength 4+ only really matters if he is doing Push or Charge special attacks, but he isn't bad at doing these. Charge especially is a nice way of getting extra damage when moving to attack, and an extra chance of knock down before attacking. It does cost 2 counters though, so cuts into what he can do in any given turn.
At defence 2 with Large, the Brute is very easy to hit. He does make up for this with endurance 7, Light Armour for a little wound penalty, and Sturdy to stop him losing huge amounts of counters. Cybernetic is a good way to keep him going as well, but the block bonus isn't huge with his defence 2
Like a few others in Militia, he comes stock with a Gas Mask to protect him from Gas attacks and traits. He has the Elite:Militia Brute trait to go with Arkham Knight's Elite Boss, but the other option is Eternal and not that good so currently it doesn't mean too much. His speed is something worth noting as well, as he is very slow for a Large model (maximum 8" movement) and as such tends to need equipment to get him going properly (Camo Vest or Neurotoxic Drugs).
Militia 2 has a Knife at attack 3 strength 5+, which means he is only putting out little bits of damage at a time and will rarely (if ever) kill something by himself in a game. Rerolls to wound is great to have, but it's a low damage weapon and won't do fantastic work. He is a cheap model though at 15 rep, so you can't expect any better.
Militia Commander 1 has 2 different weapons that serve different roles in the crew, while also being attack 4. His attack stat is largely useless though, as with no melee weapon he is only doing single stun, so he should just use his ammunition and ranged attacks when he can. He has a smoke grenade, which anyone who's read my League overviews will know I love, that can help both shut down enemy pieces and protect from ranged attacks against his crew, and for damage an Automatic Pistol. This gun is pretty good for its cheap cost, and at RoF3 blood/stun it's a little Firearm that can punch above its weight well, especially with Expert Marksman to reduce Ping! rolls against it.
At defence 3 and endurance 4/5, they're fairly easy to take out.
Like all Militia Troopers, they both have Veteran to push counters around, which helps a lot with willpower 4 and 5. Militia 2 has a Gas Mask which is great to have when Scarecrow is around, while the Commander has Kill Them! which is a great way to boost up other henchmen, particularly the melee ones (anything with a Baton weapon)