Acacia - [Redacted]

If you don't have [Redacted] yet but want to try her out, she is available as a Trial Operative in Story Chapters 6-8.
You can also try her out as a Trial Operative in Star Master at max level and with a good weapon, great logistics, max Neuronics/Deiwos, and max Manifestations.

[Redacted] can rapidly throw out daggers that bounce between targets and deal respectable damage, which generally makes her the best 4* operative for dps against groups.
As a support operative, she can also inflict slow, which can be useful, although she's not a good support evem when compared to the other 4* operatives.

She's one of the best 4* operatives for group dps, however she isn't as good for single-target dps, and she doesn't do much as a support, meaning Acacia isn't a commonly used 4*.
If you only have 4* operatives and want to build two teams, Acacia dealing skill damage means she's a good choice as your 2nd teams dps with Chenxing and Marian working well as her supports, although her single-target dps still isn't brilliant, whilst also potentially having problems with sustaining her S-Energy over longer fights.

The Basics

Role:
Early-mid game: Main DPS
Late-end game: Slow support and buffer
Deals Chaos Damage
Weapon Type: Pistol
Deals both ballistic and skill damage
Mobility is good

How to use Acacia - [Redacted]

As a DPS:
1. Spam her standard skill as often as you can
2. Otherwise just kite and shoot.

As a Support:
Just spam her support skill off-cooldown.

How to build Acacia - [Redacted]

Weapon:
As a DPS: Star Ocean / Nexus.
As a support: Prismatic Igniter.
Weapon Parts: Max ATK
Logistics Squad:
As a main DPS: Thebes / Twilight
+10.0% ATK
2x S-Energy Recovery and 1x Skill Haste
+8.5% Chaos Damage
As a support: Navigator
+10.0% ATK
+19.3 Skill Haste
+8.5% Chaos Damage.
Best squadmates:
With Acacia as a main-DPS:
Chenxing - The Obeserver
Marian - Queen of Pain
With Acacia as a support:
[Redacted] can support all DPS operatives

Standard Attack

[Redacted]s attack is a regular attack, although the high Compatibility rating of her revolver means she does deal quite high damage per shot, albeit at a low rate of fire.

Standard Skill

[Redacted] throws a dagger that deals chaos damage to the target, and bounces to other targets, hitting up to 6 times, and a max of 3 times per target.
Each bounce reduces the damage by a stacking 10%.

By-default this skill uses 4 S-Energy with a cooldown of 4 seconds, which means that if you spam it you'll recover S-Energy as fast as you use it.
(Operatives recover 1 S-Energy per second by-default.)

With her Neuronic buff, the cooldown is reduced to 3s.
This does allow her to spam her skill more often, but over long fights her damage will be limited by her S-Energy regen, as using 4 S-Energy every 3s means she will eventually run out of S-Energy, at which point her dps drops back to the same as without the Neuronic, as she's limited by her S-Energy regen rate.

With her other Neuronic, any member of your team inflicting a control effect recovers 1 S-Energy for [Redacted].
[Redacted]s ultimate ability does inflict a control effect [Slow] but beyond that [Redacted] doesn't have any way to inflict a control effect.
You can use your other operatives support skill to inflict control effects, but overall this Neuronic is a very low increase to her sustain, generally speaking - over medium-long fights she will still run out of S-Energy.

Ultimate Skill

[Redacted]s ultimate skill creates a PBAoE around herself that slows all enemies and enemy projectiles.
This has a 6s duration, a U-Energy cost of 100, and a cooldown of 100 seconds, which means that uptime is extremely low.

With her Neuronic buff, the PBAoE gives a +10% ATK buff, which is nice, but since it only applies during her ults 6s duration, its uptime is low.

With her other Neuronic buff, [Redacted]s standard skill has no cooldown in her ults PBAoE.
Since it still uses S-Energy, if you are using [Redacted] as your main dps this is unlikely to do much for your dps, as that is still entirely limited by your S-Energy regen anyway.

Support Skill

[Redacted]s support skill throws a dagger that deals good damage and slows for 5s

With her neuronic buff, it will also slow all targets in a PBAoE around the main target.
With her other neuronic, it deals +100% Chaos DMG to all the targets damaged.
These two neuronics combine to mean the AoE damage is actually quite good, however having a 25 second cooldown means the actual dps isn't great.

Weapon

As a DPS:

Star Ocean
Increases Skill Dmg by a good amount.
When an active skill hits a target, it deals an extra 9% ATK every 0.5s, for 3s, for 18%/s, or 54% overall over the 3s.
Repeated hits simply reset the duration.
This doesn't stack.
Given that [Redacted]s standard skill has a cooldown of around 3s, you can generally keep this damage up all the time.
Her standard skill deals 30%, so Star Ocean deals an extra 60%.
Star Ocean is a huge damage buff for [Redacted].
Note that Star Ocean deals Kinetic damage, not Chaos damage, which can make it difficult for Acacia to use type-specific buffs, but it's still generally her best weapon.
The main type-specific buffs are Marian - Queen of Pain's Support Skill, and Vidya - Celestial Swan's Support Skill.
Nexus
Gives a 6% Standard Skill DMG boost for the each of the first 6 seconds of combat, for 36% Standard Skill Damage total.
Since a large percentage of Acacia's damage is in her standard skill, Nexus is a large boost to her damage
If you need Acacia to only deal one type of damage (i.e. for her gun to deal Chaos-damage), then Nexus is her best weapon.

As a Support:

Prismatic Igniter
Gives the deployed operative an ATK buff for 15s after the operative with Prismatic Igniter uses their support skill.

Logistics

Acacia is a 4* operative, so don't waste your re-rolls on her - save them for your 5* operatives.

As a DPS

[Redacted]s best logistics squad is Thebes.

Thebes gives a +2% ATK buff for 5s every time a standard, ultimate, or support skill hits a target.
Since [Redacted] uses her standard skill very frequently, and can hit a lot of targets each cast, Thebes can give [Redacted] a strong ATK buff.

Thebes also increases [Redacted]s Skill DMG by 24%, which is good.

Twilight is also a great squad for Acacia, as her Standard Skill is an Active Skill which hits often enough to maintain Twilight's -16% Resistance Debuff.

For stats [Redacted] wants +10.0% ATK and +8.5% Chaos Damage.

Alignment Index gives initial U-Energy when the stage starts, which doesn't help her sustained dps at all, and hence isn't a good choice.

For her 2nd basic stat you'll want some combination of Skill Haste and/or S-Energy Recovery.
I'd generally recommend 2x S-Energy Recovery and 1x Skill Haste.

As a Support

Navigator
Inflicting a control effect increases the damage the target takes for 10s.
Since [Redacted]s support skill always inflicts a control effect (Slow) Navigator always triggers whenever she uses her support skill
Twilight
After dealing damage with a support skill, reduces the targets resistance to that damage type for 5s.
Since [Redacted] deals Chaos damage, Twilight is only useful to buff dps operatives who deal chaos damage.
The long cooldown of [Redacted]s support skill means that the much higher uptime of Navigator makes that the better squad overall.
Amarna
Gives a 30% Ballistic Damage buff for 15s after using a support skill, which is pretty strong.
If supporting a ballistic DPS, Amarna is a strong choice, however since damage taken modifiers are generally stronger, Navigator is usually the stronger squad overall.

For stats:
If using Prismatic Igniter, Acacia wants +10.0% ATK.
Skill Haste is the next best stat.
For the 3rd stat, you want +8.5% Chaos Damage
If using Prismatic Igniter you thus want ATK, Skill Haste, and Chaos Damage

If not using Prismatic Igniter, you want Skill Haste, Chaos Damage, and then generally S-Energy Recovery or Alignment Index.
S-Energy Recovery helps with sustain over longer fights. For shorter fights Alignment Index is generally the better stat.

Manifestation

M1 causes [Redacted]s standard skill to mark targets for 3s, which causes shots against the target to deal extra Chaos damage.
The damage isn't overly high (2.5%) but once you've used Acacia's standard skill it's basically a permanent damage buff.
M2 increases the number of marks from M1 to 5.
This means [Redacte] deals an extra 2.5*5 = 12.5% damage per shot, which is actually decent.
[Redacted]s damage per shot is already high due to her revolvers very high compatibility stat, so this isn't a massive damage buff, but it's respectable.
M3 increases the damage of [Redacted]s standard skill by 1% per bullet remaining in her magazine>
Due to her revolers low magazine capacity, this isn't a massive damage buff, but is useful due to how much of her damage comes from her standard skill.
M4 gives +1 skill level to her standard skill, increasing its damage.
M4 also reduces her standard skills cooldown and S-Energy cost to 3.8, which is a good bonus to her sustain and dps.
M5 increases the number of targets her standard skill can hit from 6 to 9.
The number of hits each individual target remains the same, but M5 is a large damage bonus against groups.

Being a 4* operative, you'll max [Redacted] eventually.

Good Teammates for Acacia - [Redacted]

[Redacted] can work as a 4* support operative, but she isn't a very good support overall.
As such, you generally only want to use her as a support operative if you don't have any better support operatives.
Her support effects are universal though, and [Redacted] can work as a support for essentially all DPS operatives.

If you are using [Redacted] as a main DPS, then most skill or hybrid supports work well with her.
Skill dmg supports like Riptide and Freefin work well.
Hybrid supports like Exuvia can also work due to her consistent shooting and skill usage
Universal supports like Celestial Swan or The Cub work well with [Redacted]
Purely ballistic supports like Starshine aren't ideal but can work, but aptitude or per-shot buffs don't work well with [Redacted] due to her very low rate of fire.
All of those are 5* supports though, and 5* operatives tend to all deal more damage than 4* operatives like [Redacted], so if they're all you have then you're better of using [Redacted] as the support for them, not the other way around.

If you only have 4* operatives (or just don't have many 5* operatives), then Chenxing - The Observer is generally the best support for [Redacted], with Chenxing providing some quite nice skill damage buffs as well as some healing.
You can generally swap Chenxing in for single-target damage, and use [Redacted] against groups, which works well, and they pair well together.

Marian - Queen of Pain is also a fantastic support for Acacia, with Marian's Support Skill providing a -20% chaos damage resistance debuff to unshielded enemies, which will increase Acacia's damage to a good degree. If using Marian to support Acacia, you want to give Marian Deep Sea's Call instead of Disco Confusion.
Since Chenxing doesn't deal Chaos damage and thus isn't buffed by Marian, if using Acacia + Chenxing + Marian, you want to use Acacia as your main dps only.

Overall

Overall, [Redacted] performs well against groups due to her daggers bouncing between targets, which gives her good dps [for a 4* operative] when going up against groups.
She pairs well with Chenxing - The Observer, who can provide her with strong skill damage buffs and some healing, as well as Marian - Queen of Pain who debuffs enemies chaos damage resistance, which makes for a good team if you only have 4* operatives available or just don't have many 5* operatives yet.