If you don't have Lyfe - Infinite Sight yet but want to try her out, she is available as a Trial Operative in Story Mission 13-12
Overall, Lyfe IS is a pretty easy operative to play, having high damage, high mobility, and high survivability, although her constant movement and dodge spamming can get annoying after a while, especially in small spaces.
Role: Main DPS
Kinetic Damage
Deals primarily ballistic damage
Great mobility
High damage
Constantly dodging gives good mobility
High mobility gives good survivability
Ultimate Ability is useless against single-targets
I.e. Literally all endgame content
Only shooting makes her monotonous to play
Almost entirely single-target damage
She needs quite a lot of button mashing
She is constantly moving
1. Use her standard skill off-cooldown
2. If your dodge shot is full, use it (but reload first if you don't have the ammo for it)
3. Hold down left click
Use her Ultimate against large groups only - never against single targets
TL:DR: Hold down left click, dodge when the gauge is full, and use your standard skill off-cooldown.
Standard Attack
IS' standard attack deals damage and also charges up her Dodge Shot.
Dodge Shot
When the gauge is full, IS' next dodge will be a Dodge Shot.
This will shoot 10 bullets extremely quickly, dealing high damage, and with auto-atm.
The base damage of her dodge shot is affected by her Crit Rate and RoF.
Most of IS' damage comes from her dodge shot.
Dodge Shot sufferrs a massive damage penalty if IS doesn't have enough bullets to fully use it.
If IS doesn't have enough bullets to do a full Dodge Shot, then reload first so you don't waste its damage.
Lyfe IS' dodge is not an actual dodge - she can't be interrupted during it and gains 50% damage reduction, but is still vulnerable.
Nonetheless, her dodge is a large survivabiliy increase.
The dodge moves in the direction IS is already going in. If stationary, she moves forwards.
This means that you probably want to keep IS moving, otherwise you'll just keep moving closer to your target as you spam her Dodge Shot.
Since it always crits, CRIT Rate buffs instead give her Dodge-Shot an equivalent amount of Ballistic damage.
Since it has a fixed rate of fire, RoF buffs instead give her Dodge-Shot an equivalent amount of Ballistic damage.
Standard Skill
IS' standard skill deals kinetic damage and marks an enemy with an Insight Mark, causing it to take additional damage on top of her Dodge Shot.
Shooting an enemy with an insight mark also causes IS to get extra Dodge-Shot charge per hit.
Using IS' Standard Skill will fully recharge her Dodge Shot, so if her Dodge Shot is already full, use the Dodge Shot before using her skill.
Basically just spam her Standard Skill off cooldown.
Ultimate Skill
IS' Ultimate Skill causes her to deal PBAoE damage over a massive radius.
This is absolutely fantastic for taking out groups, but it is a hefty DPS loss against single-targets, so don't use her Ultimate when bossing.
This does mean that against bosses IS doesn't need or want U-Energy, allowing a support operative to make full use of it.
There are only three Dual SMGs in the game - the green 3* one she comes with by-default , the 4* event weapon (Revolving Glow), and her 5* (Nightborne Crown).
Obviously her 5* is best, and her 4* is better than the 3*. Simple.
For weapon parts - you have a Hobson's choice as there's only one option for each slot - equip them, or don't.
So equip them if you have them.
Use Nova 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% Kinetic Damage
Alignment gives her more ATK, and is her best second stat (After ATK)
Crit DMG isn't too bad, as her dodge shot (where most of her damage is) has a 100% chance to Crit.
Crit DMG is thus a decent cope-stat though if you have a good roll for it and don't want to spend the resources to re-roll it.
Since her dodge-shot always crits, crit rate only affects the crit rather non-dodge-shots, which are a minority of her damage.
Crit Rate buffs do give an equal amount of dodge shot damage.
This means a max-roll crit rate mod gives +5.3% dodge shot damage, whereas a max-roll alignment index gives dodge shot +10.6% damage buff - literally twice as much.
M1 increases the Final DMg of her Dodge Shot by 20%, as well as making her dodge shot not reduce stamina.
Her Dodge Shot not reducing stamina is a very nice QoL feature
Most of Lyfe's damage comes from her Dodge Shot, so a 20% Final DMG bonus for it is still a large increase.
M2 Lyfe gains 20 Dodge-Shot Charge after she Dodge Shots
Since a Dodge Shot takes 60 Dodge-Shot Charge, this allows her to need to only gain 40 charge to Dodge-Shot not 60, for a 1/3rd damage increase for her Dodge Shot.
M3 gives Lyfe 12% more Ballistic DMG to targets with 1 insight mark. For each extra insight mark increase it by an extra 3%.
Insight Mark has an 8s cooldown and a 10s duration, so an insight mark should always be active.
M4 increases Lyfe's Standard Skill level by 1, increasing its damage, as well as increasing the additional damage Lyfe IS' Dodge-Shot to an enemy with an Insight Mark.
The extra damage is a 10% increase.
M5 gives Lyfe IS 20% increased Kinetic DMG when equipped with a Kinetic weapon (I.e. hopefully always)
All of Lyfe IS' Manifestations increase her damage by a decent amount.
If you want efficiency (good damage with minimal investment), then I'd say M3 is a good stopping point.
Lyfe IS works well with most of the games stronger support operatives:
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.
Nightglow
Lyfe IS can make full use of Nightglow's ATK, Ballistic, and crit buffs, and Nightglow is a fantastic support for Lyfe IS.
Note that Nightglow is off-element to Lyfe IS (Nightglow deals Electrical damage)
Phantasia
Phantasia adds Frost Damage to each shot. Given that Lyfe IS has a high fire rate this adds up to a lot of damage.
The increased ballistic damage of Tess' ult is also nice.
Again - Phantasia is off-element to Lyfe IS (Phantasia adds Frost damage) and adding it per-shot means for IS Phantasia and Celestial Swan are utterly incompatible.
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
Her Dodge-Shots auto-aim means that Lyfe IS doesn't care that much about the utility of not having to aim, and the extra damage is nice.
Note that Shadow Ka is off-element to Lyfe IS (Shadow Ka deals Chaos damage)
Lyfe IS' best supports are Celestial Swan and Nightglow, although since Nightglow is off-element to Lyfe IS you won't want to use both of them together.
Cope Supports like Agave, [Redacted], Quiet Quitter, etc. are still fine, but Bubu's best supports are Celestial Swan and Nightglow - Mauxir isn't as mechanically strong, but if she helps you land more shots against tricky bosses then she will likely be your best support.
Since Bubu reloads automatically and has a tiny magazine size, Fenny - Starshine is a poor support for Bubu.