Cherno - Enigma

Cherno - Enigma is not currently available as a Trial Operative in any story mission, so if you don't have her the only way to try her is to wait for her banner so she has a trial.

Enigma deals good damage against stationary enemies, but performs poorly against highly mobile enemies.
Whilst Enigma used to be the games best dps, powercreep has not been kind to Enigma, with a large number of newer operatives doing notably more DPS than her, yet without the poor mobility and ineffectiveness against mobile enemies that Enigma faces.
Enigma also has the disadvantage that her low ballistic damage plus very few skill casts means she doesn't synergize with several of the strong new support operatives.

The Basics

Role: Main DPS
Chaos Damage
Deals almost entirely skill damage
Mobility is not great

Advantages

Works very well against stationary enemies
DPS is good
Deals some DoT damage as well.

Disadvantages

Near-useless against moving enemies
Powercreep do be a thing...
Her ult is pathetic compared to her standard skill
Most of her damage is in her Skill detonation
This makes her slow to start dealing damage
Doesn't really benefit from S/U-Energy buffs
Her ult can feel clunky to use

How to use Cherno - Enigma

1. When the Enmity gauge on the enemy is full and you have three Voids up, hold her standard skill to detonate all three Voids
2. Cast her ult immediately after detonating her standard skill
3. Cast Enigma's standard skill off-cooldown
4. When not casting her standard skill, shoot enemies
Repeat

Standard Attack
Enigma's standard attack deals damage and also inflicts 2 Enmity stacks on the target.

Enmity Stacks
Enmity deals Chaos DoT damage to enemies every 0.5 seconds.
With lots of Enmity stacks the dps is not awful, but Enmity is primarily used as fuel for her Standard Skill detonation.

Enemies inflicted with Enmity have a gauge on them to show how much Enmity they have.
The max # of Enmity stacks an enemy can have is 300.

With the max of 300 Enmity stacks enemies will be taking 30% * 300 * 0.1% = 900%% = 9% of Enigma's ATK per second.
With the usual 600 Alignment Index, this is increased to 60% * 300 * 0.1% = 1,800%% = 18% of Enigma's ATK per second.
Over Enigma's entire rotation, halve those amounts to get the average amount of damage they deal.

Enigma's Enmity represents a very small part of her overall damage.

Standard Skill
Tapping Enigma's Standard Skill creates a large Void on top of the target enemy.
This Void continuously deals PBAoE Chaos damage to enemies touching it.
Enemies damaged by a Void are also inflicted with an Enmity stack.
30 stacks upon creation of a Void. 1 stack per second to enemies standing in at least one Void.

Enigma can only have 3 Voids at a time - if another is created beyond that the new Void will replace the oldest existing Void.

Holding down Enigma's standard skill detonates all her Voids, dealing very high Chaos AoE damage around each Void as well as around Enigma herself.
The damage of the detonation is entirely determined by how many Enmity stacks the target has.
Detonating 3 Voids against enemies with max Enmity stacks is where the vast majority of Enigma's damage comes from.
Detonating her Voids removes all Enmity stacks from all enemies.

Note that Enigma's standard skill grants 30 Enmity stacks and casts quicker than Enigma can shoot 15 bullets (2 Enmity/bullet *15 bullets = 30 Enmity)
(or 10 bullets with M1 - 3.2 Enmity/bullet = 9.375 bullets)
(Remember that since it's an average, you have to include the time needed to reload those bullets as well.)
This means that you should spam her Standard Skill as often as you can, as this is the fastest way of building up Enmity stacks.

Detonating resets the skills cooldown, so you can create another Void immediately after detonating.

Detonating her standard skill forces Enigma to remain stationary for a few seconds.
Combined with Enigma slowing down when she casts a regular void, this makes her overall manoeuvrability pretty poor.

Ultimate Skill
Enigma deals AoE chaos damage and inflicts 100 Enmity stacks on enemies hit.
If she has less than 3 Voids, she creates more until she has 3 Voids active.

Note that Enigma's ult deals around 8-10% of the damage of a full-Enmity 3-Void standard skill detonation.
Her Ult is a flat 1000% + 756 damage
Her standard skill is 9% * Enmity stacks * 3 voids (or 4 if Enigma herself is nearby) = 9% * 300 * 3 or 4 = 8,100% or 10,800%
(More still with Manifestation levels...)
As such, you are better off fitting her Ult into her standard skill rotation - use her Ult when she has zero voids to speed up her standard skill rotation.
The extra damage from delaying her ult until she has zero voids, thus not having to create Voids with her standard skill, thus allowing her to shoot more and inflict more Enmity, thus using her detonation more often, does usually result in more total damage than casting the ult immediately off-cooldown.

Her ult being used as a battery for her Standard Skill can make her ult feel clunky to use.

Support Skill
Enigma's Support Skill knocks the target into the air and inflicts them with Shimmer, which causes them to take extra Chaos Damage.
Note that this is not a per-shot effect that can repeatedly trigger, and like most Main-DPS-ers you really don't want to use Enigma as a support operative.

Weapon

Uninvited Adieu
Her 5* weapon, and her best weapon.
100 Battle Veteran
Cherno has decent magazine capacity and spends most of her time in combat magdumping, so she gets a lot of use out of 100BV
Uninvited Adieu is the better weapon for her, but 100BV is still very good.
Halo of Hope
Her 4* weapon.
Enmity counts as Dazed, so Enigma gets a lot of damage out of the bonus as Halo of Hope will be at max stacks most of the time in combat.
With a proper rotation, Halo of Hope affects literally of of Enigma's damage with maximum effect.

Logistics

Use Dziady squad - it was designed specifically for her and is her best choice.

For stats you want +10.0% ATK and +106 Alignment Index.
For the Special talent, you want 8.5% Chaos Damage

Alignment is useful, but not nearly as strong for Enigma as ATK is, as Alignment only boosts her Enmity damage, not her Standard Skill or ult or ballistic damage.

Since most of her damage is in her skills, and skills can't crit, crit mods aren't useful to Enigma.
Enigma also isn't limited by S-Energy, and her ult doesn't deal enough damage for U-Energy recovery to be worth it.
Just go with ATK and Alignment, really - everything else just doesn't do much/anything for her.

Manifestation

M1 gives her shots a 60% chance to add an extra Enmity
This adds up to a lot of extra Enmtiy, speeding up Enigma's rotation a lot, and thus improving damage a lot too.
+30% Final Damage for her Standard Skill detonation
Most of her damage comes from her Standard Skill detonation, so this is a huge buff.
For each 60 Enmity, the target has, it takes 1 additional instance of Chaos Dmg equal to 150% of Cherno's ATK.
This is quite a nice damage boost for her Enmity, but doesn't affect her Standard Skill detonation which is where most of her damage is.
An extra 150%*5 = 750% damage per rotation though is nice, albeit not a huge percentage increase.
10% damage increase for her Standard Skill detonation (9% -> 9.9%)
Also increases the skill level, increasing damage further.
Given how much of her damage is in her Standard Skill detonation, this is a nice increase.
If Enigma's Standard Skill detonation doesn't kill the target, it gets an extra 50 Enmity applied to it.
This is quite nice, but is of course only useful against bosses that can actually survive an M5 Enigma's Standard Skill detonation anyway, which means endgame bosses.
This will speed up her rotation against endgame bosses noticeably though.
Given that she should always detonate at the max of 300 Enmity, She goes from needing 300 Enmity for her standard rotation to needing 250, so enemies just getting 50 Enmity is in essence a 1/6th Final Damage Bonus, which is very nice.

For max damage you'll want M5.
For maximum efficiency M2 is a natural stopping point for Enigma, providing a large damage bonus, whilst later Manifestations are lesser increases.

Good Supports for Cherno - Enigma

Enigma is primarily a Skill DMG operative, and hence synergizes well with Skill dmg buffs:

Vidya - Celestial Swan (and other resistance shredders)
Celestial Swan and other resistance shredders (Acacia - Kaguya, etc.) that reduce the enemies resistance help enemies take more damage.
If using Celestial Swan, make sure the other support isn't off element to the main DPS.
Marian - Riptide
Riptide's Skill DMG buffs work well with Enigma.
Riptide is also on-element to Enigma, so you can use Enigma + Riptide + Celestial Swan if you wish.
Enya - Exuvia
Cherno easily proc's Enya's buffs due to her frequent shooting, and appreciates Enya's Skill DMG buffs.
Eatchel - The Cub
A Blitzing Fangs Eatchel provides healing as well as a decent ATK buff.
Not the strongest support, but still good.
Mauxir - Shadow Ka
More damage, and a target that doesn't move.
Sadhow Ka is also on-element to Enigma, so you can use Enigma + Shadow Ka + Celestial Swan if you wish.