The Soulkiller meta
I've just finished leveling all my commanders for Soulkiller. Still haven't won an insane match, still playing loads of matches with teammates doing dumb stuff, so thought I'd offer my take on ideal strategy so we can start collecting some wins on insane. FYI this is specific to hard/insane difficulty, as easy/normal you can win without much trouble. Real gameplay strategy is at the end.
BB: Iron Gale
Fairly typical brawler BB gameplay. You are tanky, but can get easily deleted if showing your broadside to enemy BBs. When fighting enemy BBs at mid-close range, stay bow-in and don't over-maneuver trying to get that third turret firing. Only go broadside to cruisers. Don't bother shooting enemy DDs unless there's no other targets--your blue cruisers and DDs can shred them much more effectively, even if you're shooting HE. YOUR torpedoes have a fairly quick reload so pop them whenever you get a chance.
You should be pretty balanced between AP and HE--only use HE on bow-in targets, as even cruisers can ricochet most of your shells. Your HE still has great damage output.
Stay ahead of your cruisers, they are squishy. It's okay if a DD wants to get ahead of you, but don't let them get too far away. Your DDs don't have heals, so try to heal them whenever possible.
DODGE TORPS! Don't rely on your hydrophone to bust torpedoes--the cooldown is long and you can easily get hit with staggered waves of torpedoes. Dodge whenever possible and save hydrophone for emergencies. Don't ever pop it preemptively, as you should be able to guess when torps are coming by keeping an eye on enemy DDs.
Save your battle upgrades for heals as you'll most likely need them. Unless you catch some citadels, you shouldn't need any of them until at least the second half of the match.
Cruiser: Ether Tempest
Stay at range, behind your BBs. You're not a tank, you're not super maneuverable, and you have no smoke, so getting within 7km of an enemy cluster can be deadly, especially a red BB. You can tank enemy fire bow-in fairly well if you must, but you'll only be able to use half your guns.
Damage BBs by shooting superstructure. Damage cruisers by shooting broadside if you're close-mid range, but otherwise aim superstructure. You should have no problem killing DDs.
Like with BBs, try to dodge torps as much as possible, and keep an eye on red DDs to anticipate them. Save your hydrophone for emergencies only. Also, like with BBs, make an effort to keep your DDs healed when you can. Your torps are effective but don't have great angles or range, so you'll likely only be able to use them safely on ships coming out from behind an island—don't go broadside in the middle of a lane just to get torps away, unless if you have the torp range mod and can do so from long distance.
Like with BBs, save your battle upgrades for heals, unless you're at the final boss.
DD: Night Shard
This is the trickiest of ships to play and the most crucial. You have the most damage potential (based only on my experience) yet it's the easiest to whiff by firing torps at a ship which your teammates kill before they hit, or by just having your homing torps curve into a rock. Only send torps when you're confident they'll land: opt for sending one salvo at a ship instead of two, as it'll likely take damage from your teammates before they hit. Be aware of your teammates so you don't waste torps by hitting them, and of enemy ships who might die in the path of your torps.
Use your guns! Your guns will do serious damage on enemy cruisers and especially DDs. Your smoke has a fast reload, so your strategy for each wave should generally be to 1) get torps in the water, 2) smoke up (bonus points if you can conceal a friendly cruiser as well), 3) use your guns to kill any DDs or cruisers, or chip away at BB superstructures. Also don't forget your radar which is crucial if you smoke up ahead of all your teammates.
Don't get so far ahead of your teammates that they can't heal or support you. You're no use to your team if you die, or have to run away to the side of the map.
STRATEGY
First wave
One BB will have broadside angle on the incoming boss and cruisers--fire AP at them. The other BB should use its HE. Cruiser(s) should aim to take out the enemy cruisers and DDs, WITHOUT moving too far forward to be singled out by the enemy. DDs: you should be able to get torps off at capital ships while also smoking up and helping to clear enemy DDs, but your main goal here should just be to push as far forward so you can lead the charge into the second wave as soon as possible. Don't be caught far back or facing backwards once the first wave is cleared.
Middle waves
CRUCIALLY, your team needs to advance from both the left and the right after the first wave, ideally with a BB on each side, and without any teammate getting stuck alone. If everyone advances up one side, you'll run the risk of a red ship advancing the empty flank, and you'll have to spend time chasing them down before advancing to the next wave. This will also set you up for crossfires on the third wave.
DD(s) should lead the charge, and should be far enough forward to get torps on the second boss before it moves behind the island. Smoke up after firing torps and start shooting enemy DDs, then cruisers. BBs should be close behind or next to DDs.
Positioning is everything. If your team is distributed well across both flanks, you should be able to advance to the final wave without any blue ships getting singled out and destroyed. It's very easy to lose a match by running out of time, so keep advancing as quickly as possible without getting separated from your team.
Final boss
If you have any battle upgrades remaining and you aren't about to die, now is the time to upgrade damage/reload. You may only have 2-3 minutes to kill the final boss, so you need to be putting out as much damage as possible. THIS ESPECIALLY APPLIES TO DDs, and this is where having a surviving DD can completely make or break your match. A single DD with fully upgraded damage/reload can drain half the final boss' health in 1-2 minutes. You only have to kill the boss, so ignore any red ships unless they're getting too close to you—enemy ships WILL ram you.
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Alright that's it. I drafted this pretty quickly and tried to keep it as brief as possible, but will likely keep refining it or adding any suggestions y'all throw out. Let's complete some challenges.