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Borderlands 4
CHROMA Radiation Harlowe Boss Farm Build
☆ How Rush Saved Mercenary Day (Bounty Pack 1)
★ 12 active SHiFT Codes as of December 4, 2025
☆ Black Market Location
★ Elemental Weakness Chart
☆ Legendary Weapons
★ Builds: Vex | Amon | Rafa | Harlowe
The CHROMA Radiation Harlowe build focuses on making Harlowe shoot her CHROMA Accelerator frequently to easily farm bosses in Borderlands 4. See the best builds, skills, weapons, and gear to use for Harlowe, along with the best skill tree abilities and character playstyle.
| All Harlowe Guides | ||
|---|---|---|
| Best Builds | Cosmetics | Skill Trees and Voice Actor |
| Leveling Build | Boss Farm Build | Cryo Stasis Build |
List of Contents
CHROMA Radiation Harlowe Strengths and Weaknesses
Strengths and Weaknesses
| Strengths | Weaknesses | ||||
|---|---|---|---|---|---|
|
✔︎Very high status damage ✔︎Great for Mobbing ✔︎Easily destroys Badasses and Bosses |
✖︎Extremely Skill reliant ✖︎Requires specific end-game gear and rolls ✖︎Struggles against Elemental Eaters |
Harlowe's CHROMA Radiation Build focuses on dealing status damage, built around her Rocket Scientist Class Mod. Due to the sheer amount of status effects that can be applied when using Katagawa's Revenge, this build makes it very optimal for mob clearing or Boss Farming.
The build's weaknesses also revolve around its strengths, with its glaring weakness being its skill and status damage reliance, leaving you weak without your Action Skill, and against enemies with elemental immunities, such as Elemental Eaters.
CHROMA Radiation Harlowe Best Skills
Best Action Skill
| Action Skill |  CHROMA Accelerator |
|---|---|
| Skill Tree: Creative Bursts | |
The CHROMA Accelerator shoots an Unstable Energy Pocket that deals Cryo Damage to enemies it grazes before exploding and dealing Radiation damage in a large area. This explosion can be triggered manually or automatically if the pocket hits a surface.
This makes the CHROMA Accelerator perfect for both taking down bosses and clearing out groups of enemies.
Best Passive Skills
Creative Bursts
Seize the Day
 | |||
| Skill Tree | Priority Skills | ||
|---|---|---|---|
| Creative Bursts |  Field-Ready Prototype Harlowe gains increased Action Skill Damage.  Elementary Harlowe gains increased Elemental Damage and Status Effect Damage.  Test Subjects Whenever Harlowe applies a Status Effect to an enemy, she gains increased Action Skill Cooldown Rate.  Enriched Harlowe gains increased Radiation Damage.  Practical Applications Harlowe gains increased Skill Damage.  Poisoned Sun Harlowe gains increased Radiation Damage and Irradiation Chance.  Fissile Launcher Whenever Harlowe damages an Irradiated enemy or an Entangled enemy, shoot a Radiation Dart at another enemy.  Chain Reactor Harlowe deals Bonus Radiation Damage to Entangled enemies.  Dirty Bomb Whenever Harlowe Irradiates an enemy, create a Radiation Explosion on that enemy.  Mechanical Brilliance Whenever Harlowe damages an enemy with a Skill, she gains increased Skill Damage. This effect can stack. | ||
 | |||
| Skill Tree | Priority Skills | ||
|---|---|---|---|
 Seize the Day |  Pulse Drive Harlowe gains increased Action Skill Cooldown Rate.  Make Extraordinary Harlowe gains Critical Hit Chance with all Skills. This chance increases every time Harlowe Entangles an enemy. This effect can stack. | ||
The best skills for the CHROMA Radiation Harlowe Build revolve around maximizing Skill and Radiation damage, as well as improving the Action Skill Cooldown Rate to shorten the space between your burst windows.
Recommended Skill Progression
| Recommended Skill Progression | |||
|---|---|---|---|
|
Field-Ready Prototype Harlowe gains increased Action Skill Damage.
Lvl 2 |
Field-Ready Prototype Harlowe gains increased Action Skill Damage.
Lvl 3 |
Field-Ready Prototype Harlowe gains increased Action Skill Damage.
Lvl 4 |
Field-Ready Prototype Harlowe gains increased Action Skill Damage.
Lvl 5 |
|
Field-Ready Prototype Harlowe gains increased Action Skill Damage.
Lvl 6 |
Elementary Harlowe gains increased Elemental Damage and Status Effect Damage.
Lvl 7 |
Elementary Harlowe gains increased Elemental Damage and Status Effect Damage.
Lvl 8 |
Elementary Harlowe gains increased Elemental Damage and Status Effect Damage.
Lvl 9 |
|
Elementary Harlowe gains increased Elemental Damage and Status Effect Damage.
Lvl 10 |
Elementary Harlowe gains increased Elemental Damage and Status Effect Damage.
Lvl 11 |
Enriched Harlowe gains increased Radiation Damage.
Lvl 12 |
Enriched Harlowe gains increased Radiation Damage.
Lvl 13 |
|
Enriched Harlowe gains increased Radiation Damage.
Lvl 14 |
Test Subjects Whenever Harlowe applies a Status Effect to an enemy, she gains increased Action Skill Cooldown Rate.
Lvl 15 |
Test Subjects Whenever Harlowe applies a Status Effect to an enemy, she gains increased Action Skill Cooldown Rate.
Lvl 16 |
Poisoned Sun Harlowe gains increased Radiation Damage and Irradiation Chance.
Lvl 17 |
|
Poisoned Sun Harlowe gains increased Radiation Damage and Irradiation Chance.
Lvl 18 |
Poisoned Sun Harlowe gains increased Radiation Damage and Irradiation Chance.
Lvl 19 |
Poisoned Sun Harlowe gains increased Radiation Damage and Irradiation Chance.
Lvl 20 |
Poisoned Sun Harlowe gains increased Radiation Damage and Irradiation Chance.
Lvl 21 |
|
Chain Reactor Harlowe deals Bonus Radiation Damage to Entangled enemies.
Lvl 22 |
Chain Reactor Harlowe deals Bonus Radiation Damage to Entangled enemies.
Lvl 23 |
Chain Reactor Harlowe deals Bonus Radiation Damage to Entangled enemies.
Lvl 24 |
Fissile Launcher Whenever Harlowe damages an Irradiated enemy or an Entangled enemy, shoot a Radiation Dart at another enemy.
Lvl 25 |
|
Fissile Launcher Whenever Harlowe damages an Irradiated enemy or an Entangled enemy, shoot a Radiation Dart at another enemy.
Lvl 26 |
Dirty Bomb Whenever Harlowe Irradiates an enemy, create a Radiation Explosion on that enemy.
Lvl 27 |
Test Subjects Whenever Harlowe applies a Status Effect to an enemy, she gains increased Action Skill Cooldown Rate.
Lvl 28 |
Test Subjects Whenever Harlowe applies a Status Effect to an enemy, she gains increased Action Skill Cooldown Rate.
Lvl 29 |
|
Test Subjects Whenever Harlowe applies a Status Effect to an enemy, she gains increased Action Skill Cooldown Rate.
Lvl 30 |
Pulse Drive Harlowe gains increased Action Skill Cooldown Rate.
Lvl 31 |
Pulse Drive Harlowe gains increased Action Skill Cooldown Rate.
Lvl 32 |
Pulse Drive Harlowe gains increased Action Skill Cooldown Rate.
Lvl 33 |
|
Pulse Drive Harlowe gains increased Action Skill Cooldown Rate.
Lvl 34 |
Pulse Drive Harlowe gains increased Action Skill Cooldown Rate.
Lvl 35 |
Make Extraordinary Harlowe gains Critical Hit Chance with all Skills. This chance increases every time Harlowe Entangles an enemy. This effect can stack.
Lvl 36 |
Make Extraordinary Harlowe gains Critical Hit Chance with all Skills. This chance increases every time Harlowe Entangles an enemy. This effect can stack.
Lvl 37 |
|
Make Extraordinary Harlowe gains Critical Hit Chance with all Skills. This chance increases every time Harlowe Entangles an enemy. This effect can stack.
Lvl 38 |
Make Extraordinary Harlowe gains Critical Hit Chance with all Skills. This chance increases every time Harlowe Entangles an enemy. This effect can stack.
Lvl 39 |
Make Extraordinary Harlowe gains Critical Hit Chance with all Skills. This chance increases every time Harlowe Entangles an enemy. This effect can stack.
Lvl 40 |
Practical Applications Harlowe gains increased Skill Damage.
Lvl 41 |
|
Practical Applications Harlowe gains increased Skill Damage.
Lvl 42 |
Practical Applications Harlowe gains increased Skill Damage.
Lvl 43 |
Practical Applications Harlowe gains increased Skill Damage.
Lvl 44 |
Practical Applications Harlowe gains increased Skill Damage.
Lvl 45 |
|
Mechanical Brilliance Whenever Harlowe damages an enemy with a Skill, she gains increased Skill Damage. This effect can stack.
Lvl 46 |
Mechanical Brilliance Whenever Harlowe damages an enemy with a Skill, she gains increased Skill Damage. This effect can stack.
Lvl 47 |
Mechanical Brilliance Whenever Harlowe damages an enemy with a Skill, she gains increased Skill Damage. This effect can stack.
Lvl 48 |
Mechanical Brilliance Whenever Harlowe damages an enemy with a Skill, she gains increased Skill Damage. This effect can stack.
Lvl 49 |
|
Mechanical Brilliance Whenever Harlowe damages an enemy with a Skill, she gains increased Skill Damage. This effect can stack.
Lvl 50 |
|||
From Levels 1-30, your goal is to stack points in the Creative Agents tree (Red Tree) until you unlock Void Star and Demon Core. Once Demon Core is unlocked, with the skills leading up to it equipped, you should reach a point where you can effectively farm bosses alone.
Once you reach Level 31, get some Passive Skills from the Seize the Day tree (Blue Tree). Pulse Drive increases your Action Skill Cooldown Rate, while Make Extraordinary provides Critical Hit Chance to your Skills.
Use your last skill points to unlock Mechanical Brilliance and Practical Applications from the Red Tree. Mechanical Brilliance improves your Skill Damage whenever your Skill passes through enemies, while Practical Applications increases your Skill Damage immediately.
Best Augment
| Augment | Effects |
|---|---|
 Voidstar
|
• Instant 30% Current Health Damage • Freezes enemies it passes by • Use on solo bosses |
 Special Purpose Magnets
|
• Pulls enemies it passes by • Increased detonation damage based on the number of pulled enemies • Use on bosses with enemy summons |
Voidstar's instant 30% Current Health damage makes it a great opening attack against bosses, especially those who are alone. If you are facing bosses that summon enemies, or taking part in World Events or Drill Sites that have multiple enemies, then switching to Special Purpose Magnets is ideal.
Best Capstone
 Demon Core
|
||
| Tree |
Creative Bursts
(Branch 2) |
|
|---|---|---|
| Effect | ||
| As Harlowe's Unstable Energy Pocket travels, it shoots Radiation Darts at enemies. Whenever Harlowe Entangles an enemy while her Action Skill is active, automatically Irradiate that enemy. | ||
Demon Core provides additional Radiation damage via the Radiation Darts it shoots, while also Irradiating enemies that Harlowe Entangles while her Action Skill is active. This not only deals additional damage, but also applies a strong Damage over Time status effect on hit enemies.
CHROMA Radiation Harlowe Best Equipment
| Jump to a Section! | |
|---|---|
| Weapons | Class Mod |
| Enhancement | Firmware Sets |
Best Weapons
Best Legendary Weapon: Katagawa's Revenge
| Legendary | Gun Overview |
|---|---|
| Katagawa's Revenge |
Type: Sniper Manufacturer: Maliwan Stormcloud Legendary Mod |
Katagawa's Revenge is a Maliwan Sniper Rifle that summons damaging disks of whatever element is equipped whenever you damage enemies with it. Although it is a Sniper Rifle, you can use it unscoped in short range to make hitting the enemy easier.
These disks can apply Shock on the boss you are attacking, which synergizes well with skills in this build, such as Elementary and Test Subjects. Additionally, it synergizes extremely well with the Rocket Scientist Legendary Class Mod, which Entangles and Irradiates Shocked enemies.
Best Manufacturer: Maliwan
Maliwan weapons are the best when it comes to elemental weapons, making them a perfect fit for Harlowe. Try to aim for Radiation Maliwans to synergize well with the build's numerous Radiation damage buffs. Alternatively, if you have the Rocket Scientist Class Mod, you can also use a Shock Maliwan.
Best Weapon Type: Submachine Guns or Sniper Rifles
Submachine Guns with their high rate of fire make it easy to apply status effects, so a Maliwan Submachine Gun is perfect for Harlowe. Alternatively, if you have the Katagawa's Revenge, or a similarly strong Maliwan Sniper Rifle, you can use that as well.
Elemental Weakness Chart and Damage Guide
Best Class Mod
The Rocket Scientist Class Mod is the best Class Mod for Harlowe as it makes it easier for her to apply Status Effects on enemies, specifically Irradiated. This synergizes well with her build, creating a loop that continuously deals Radiation damage and increases Harlowe's Action Skill Cooldown Rate.
Alternatively, try to look for Class Mods that add skill points to important Passives, specifically those that increase Skill or Radiation damage, as well as those that increase her Action Skill Cooldown Rate.
Best Enhancement Mods
| Enhancement | Effects |
|---|---|
| Maliwan Enhancement | ・Synthesizer - Guns with Maliwan-licensed parts have +25% Status Effect Damage. |
As your build also deals Status Effect damage, having the Synthesizer Enhancement Mod increases your damage output as long as you keep applying Status Effects from your guns.
Best Firmware Sets
| Set Bonus | Effects |
|---|---|
| Deadeye 3/3 |
・Gun Accuracy is increased by 30% ・Gun Critical Hit Damage is increased by 25% ・Every Critical Hit grants 15% Critical Damage per Stack (5 max stacks) for 10s |
| High Caliber 2/3 |
・Projectile Speed is increased by 25% ・Gun Damage is increased by 10% |
CHROMA Radiation Harlowe Best Specializations
| Specialization | Tree and Effect |
|---|---|
 Riddle You This
|
Brute TreeWhenever the Vault Hunter deals Gun Damage, gain a Stack of Riddle You This, increasing Gun Damage. Stacks are lost if a new Stack has not been gained for a Duration. Gun Damage: +1% per Stack Maximum Stacks: 50 Duration: 6 seconds |
 Now With Caffeine
|
Daredevil TreeReduce Action Skill Cooldown whenever a Repkit is activated. Action Skill Cooldown Reduction: 25% |
 I Am A Gun
|
Daredevil Tree Action Skill Damage now benefits from increases to Gun Damage. Action Skill Damage: 50% of increases to Gun Damage. |
 A Honed Mind
|
Daredevil Tree Action Skills gain a chance to Critically Hit enemies, and also gain increased Action Skill Critical Hit Damage. Action Skill Critical Hit Chance: 5% Action Skill Critical Hit Damage: +50% |
We recommend taking the following Specializations to improve Harlowe's Action Skill by improving its damage and cooldown.
CHROMA Radiation Harlowe Boss Farming Guide
Start Fights with the CHROMA Accelerator
Upon entering the arena, immediately shoot your CHROMA Accelerator at the boss. This immediate burst of damage is a great way to start the fight, and can freeze the boss if you are using the Voidstar augment.
When shooting your first attack, try to aim at the boss's feet so that the Unstable Energy Pocket immediately explodes upon hitting the ground. If the boss is flying, adjust your aim accordingly and manually detonate the Unstable Energy Pocket.
Continuously Apply Status Effects
As the build also relies on applying Status Effects on the boss, make sure that you are continuously applying them by constantly firing your gun at them and using your grenades. This not only damages the boss, but also shortens your Action Skill Cooldown thanks to various Pasive Skills, allowing you to use it more often.
CHROMA Radiation Harlowe Build Playstyle
Optimized for Boss Farming
This Harlowe build is specifically designed for Boss Farming, putting heavy investment in Harlowe's skill and elemental status damage.
Through our testing, Normal Bosses in Hard difficulty can be cleared in less than 1 minute under optimized conditions, and approximately 1:45 for tankier bosses such as Vault Guardians, and Auger Mine Bosses.
How to Farm Bosses
UVHM Ready Build
Once you have finished the game's main campaign, you will be able to create a Level 30 character in Ultimate Vault Hunter Mode (UVHM). This build's skill progression works in UVHM, especially if you have appropriately leveled equipment stored in your bank.
It's important to note that even if you do not have the proper equipment, or have not unlocked UVHM yet, this build is still able to deal great damage. Use whatever you have at your disposal, then slowly make your way toward the final build goal.
Viable for Mob Clearing and Leveling
Thanks to its AoE Capabilities from Special Purpose Magnets and the CHROMA Accelerator explosion, this build can still be used for leveling and clearing the story.
If you are facing difficulties in using this build for leveling, you can try investing more skill points into Shield regeneration. You can also use our designated Best Build for Leveling Harlowe!
Best Harlowe (Gravitar) Build and Leveling Guide
Borderlands 4 Related Guides
Best Builds for Each Vault Hunter
All Character Builds
| Character | Build |
|---|---|
 Vex |
|
 Rafa |
|
 Amon |
|
 Harlowe |
CHROMA Radiation Build |
All Harlowe Builds
 CHROMA Radiation Harlowe
|
Cosmic Brilliance Leveling Harlowe
|
 Cryo Stasis Harlowe
|
Comment
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CHROMA Radiation Harlowe Boss Farm Build
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