Borderlands 4: Harlowe Chroma Accelerator build guide

The Harlowe Chroma Accelerator build in Borderlands 4 is all about dealing massive amounts of elemental burst damage and turning Harlowe into a tactical nuclear reactor. With the Chroma Accelerator as the primary Action Skill, Harlowe can obliterate waves of mobs and melt through powerful bosses in a short amount of time, making this one of the most powerful boss-farming builds in Borderlands 4.

Add weapons with a high rate of fire and Radiation Damage, and the Harlowe Chroma Accelerator build can sustain itself in the endgame of Borderlands 4 and in the Ultimate Vault Hunter Mode (UVHM).

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Borderlands 4: Best skill setup for Harlowe Chroma Accelerator build

Best-in-slot Action Skill

The build completely revolves around the Radiation procs of the Chroma Accelerator (Image via Gearbox Software)

Chroma Accelerator

• Cooldown: 38 seconds
• Pass-by Damage: 269
• Detonation Damage: 807

Harlowe's Chroma Accelerator fires an Unstable Energy Pocket, which passes through enemies, dealing Cryo Damage to all nearby foes. Pressing the Action Skill causes the Unstable Energy Pocket to detonate and deal heavy Radiation Damage across a larger area.

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Passive skill tree: Creative Bursts (red tree)

When combined with Harlowe's Radiation-based passive skills, the Chroma Accelerator Action Skill can easily wipe out powerful Primordials in Borderlands 4. These passives are key to turning Harlowe into a powerhouse by maximizing skill damage, Radiation Damage, and skill cooldown.

From level 1 to 30, your leveling priority should be Creative Bursts (red tree). Invest in increasing the effectiveness of your Radiation Damage till you can unlock Demon Core and Voidstar. At this point, you will be able to take down most bosses in the game.

Skill	Effect	Use
Field-Ready Prototype (5/5)	Harlowe gains increased Action Skill Damage up to 30%.	Boosts Chroma Accelerator’s overall nuking capability
Elementary (5/5)	Harlowe gains +20% increased Elemental Damage and +20% Status Effect damage.	Enhances Harlowe’s radiation explosions and status effects' damage output
Test Subjects (5/5)	Whenever Harlowe applies a Status Effect to an enemy, she gains +35% increased Action Skill Cooldown Rate for eight seconds.	More status effect application = faster cooldown rate
Enriched (3/3)	Harlowe gains +21% increased Radiation Damage.	One of the core passives for all Radiation-based builds
Chain Reactor (3/3)	Harlowe deals 18% of Damage Dealt as Bonus Radiation Damage to Entangled enemies.	Adds passive increased Radiation Damage output
Mechanical Brilliance (5/5)	Whenever Harlowe damages an enemy with a Skill, she gains +10% increased Skill Damage for 12 seconds. This increases maximum stacks to five.	Helps maintain consistent skill DPS during fights
Practical Applications (5/5)	Harlowe gains 35% increased Skill Damage.	This passive is a direct multiplier for the Chroma Accelerator’s damage output
Glow Up (5/5)	Harlowe gains 25% Critical Hit Chance with Guns against Irradiated enemies.	Increases critical hits while the Action Skills effect is in place
Poisoned Sun (5/5)	Harlowe gains +30% increased Radiation Damage and +60% Irradiation Chance.	Increased potency of Harlowe’s Radiation capability
Wasted (1/1)	Kill Skill: Killing an irradiated enemy or killing an enemy with Radiation Damage leaves behind a radiation Hazard that deals 61 damage per second for five seconds.	Adds another layer of DPS over Harlowe’s radiation bonuses

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Passive skill tree: Seize the day (blue tree)

Once you are past level 30, invest points in reducing the cooldown rate of Action Skills and increasing their crit chance.

Skill	Effect	Use
Pulse Drive (4/5)	Harlowe gains a +30% increased Action Skill Cooldown Rate.	Allows Harlowe to use her Action Skill more often
Make Extraordinary (3/5)	Harlowe gains +6% Critical Hit Chance with all skills. This chance increases by +3% for eight seconds every time Harlowe Entangles an enemy. This effect stacks up to 10 times.	Enhances the crit chance of Harlowe’s skills

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Best-in-slot Augments and Capstone

You can either use Voidstar to gain some life drain or Special Purpose Magnets for crowd-control capability (Image via Gearbox Software)

Augments

• Voidstar - Whenever Harlowe’s Unstable Energy Pocket passes by an enemy, it loses 30% of its current Total Health and becomes Frozen. It has a Max health Drain of 673.

If you want more crowd control on the battlefield, you can use:

• Special Purpose Magnets - Harlowe’s Unstable Energy Pocket pulls enemies along as it passes by, and its detonation deals +11% increased Damage for every enemy it has already hit.

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Capstone

Harlowe's Demon Core grants you both increased Radiation Damage and Active Skill cooldown rate (Image via Gearbox Software)

• Demon Core - As Harlowe’s Unstable Energy Pocket travels, it shoots radiation Darts at enemies with 336 damage. Whenever Harlowe Entangles an enemy while her Active Skill is active, automatically irradiate that enemy. Active Skill Cooldown is 42 seconds.

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Best equipment loadout for the Chroma Radiation Harlowe build

Recommended weapons (ARs and Sniper Rifles)

Katagawa’s Revenge is the best option for proccing Chroma Accelerator's effects (Image via Gearbox Software)

1) Katagawa’s Revenge

• Stormcloud (unique perk) - The gun’s unique perk allows it to deal both Shock and Incendiary damage, making it perfect to shred enemy armor and shield penetration.

If you want a faster weapon system, you can opt for:

1) Lucian’s Flank

• Trample (unique perk) - Critical hits refill Ammo to the gun’s magazine, making it highly sustainable in lengthy fights.

2) Aegon’s Dream

• Prophetic (unique perk) - It fires both Cryo and Incendiary ammo, making it suitable to synergize with the Chrome Accelerator Action Skill.

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Best-in-slot class mod

The Scientist and Katagawa’s Revenge work in tandem to shock enemies and spread radiation (Image via Gearbox Software)

1) Scientist

• Whenever Harlowe Shocks an enemy, she automatically Entangles and Irradiates them. Whenever she Entangles an enemy, Electric Arcs shoot out from them at other nearby foes.

Harlowe's Scientist Class mod always grants the following:

• +25% Action Skill Cooldown Rate
• +35% Splash Damage

Alternatively, you can use Atomic Driver, which amps up the Chroma Accelerator skill by draining your own health, making it a high-risk, high-reward mechanism. You can also use the Ultimate Bio-Robot, which creates alternating Cryo Hazards and Radiation Hazards.

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Best-in-slot enhancement mods

1) Maliwan Synthesizer - Guns with Maliwan-licensed parts have {mod} Status Effect Damage.

2) Bullets to Spare (2/3)

• Gun fire rate is increased by 5%.
• Gun magazine size is increased by 20%.

3) GOOJFC (3/3)

• Action Skill Cooldown Rate is increased by 10%.
• Action Skill Damage is increased by 15%.
• Action Skill Cooldown Rate is increased by an additional 20%.

Getting the cooldown of the Chroma Accelerator Action Skill as low as possible is key to bringing out the full potential of the build.

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Best Specializations

For the best specialization, invest in Sharpshooter and Runner trees till you can unlock Daredevil and level it up till you have A Honed Mind. Opt for Survivor and Brute to gain some much-needed survival capability.

1) Now with Caffeine (Daredevil)

• Reduce Action Skill Cooldown by 25% whenever a Repkit is activated.

2) Riddle You This (Brute)

• Whenever Harlowe deals Gun Damage, gain a Stack of Riddle You This (up to 50 stacks), increasing Gun Damage by +1% per stack for six seconds.

3) I am a Gun (Daredevil)

• Action Skill Damage now increases by 50% of the increase to Gun Damage.

4) A Honed Mind (Daredevil)

• Action Skills gain a 5% chance to Critically Hit enemies. They also gain +50% increased Action Skill Critical Hit Damage.

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Chroma Accelerator boss farming guide

This Harlow build variation is fully capable of dealing with the strongest bosses and mob-packed areas in Borderlands 4 (Image via Gearbox Software)

This Harlowe build thrives in boss encounters, capable of easily clearing most bosses in Hard mode.

The Chroma Accelerator is one of the best builds to tackle Vault guardians and Augur Mine bosses. Its high cooldown rate and Radiation procs are perfect to dominate the Ultimate Vault Hunter Mode (UVHM). Even though the build is designed to take out bosses in under two minutes, it is fully capable of going through waves of mobs.

Boss farming guide

• At the beginning of an encounter, start with Chroma Accelerator. Shoot at the feet of grounded bosses to auto-detonate projectiles on impact; against flight-capable enemies, detonate the projectiles manually for maximum damage.
• Keep applying status effects to trigger Test Subjects and Poisoned Sun to lower the cooldown of your Action Skill. This will allow you to constantly spam Chroma Accelerator during a boss encounter.
• This build is made to be played aggressively. Keep the pressure up on the enemy using your Demon Core. Always alternate between your Action Skill and weapon to deal massive bursts of explosive damage.
• For tackling mobs, utilize Special Purpose Magnets to pile them up and explode them with your Demon Core’s explosive Radiation Damage.

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The Chroma Accelerator Harlowe build allows the Vault Hunter to be the best boss hunter in its class. With the right endgame-optimized weapon and gear, this setup can easily take out a Primordial Vault boss in seconds, allowing you to farm bosses much more efficiently.

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