What to know
- Kill Skills are passive perks that activate after defeating enemies, giving temporary buffs like increased damage, speed, cooldowns, and survivability.
- Many Kill Skills, especially for the new character Vex, can stack and interact with minion deaths, not just direct kills.
- Building around these skills allows chaining effects for high DPS and cooldown refresh, essential for tougher content.
- Certain perks and class mechanics let some characters trigger their Kill Skills by other means (like critical hits or minion deaths).
Leveraging Kill Skills in Borderlands 4 turns every takedown into a chance to snowball your power and efficiency. These passives encourage aggressive play and can define how each Vault Hunter tackles both mob waves and bosses.
How do Kill Skills work in Borderlands 4
Kill Skills are passive upgrades tied to skill trees—most notably for the Vault Hunter Vex. When a kill is landed (by player or minion), these perks activate for a short duration, granting dramatic bonuses such as extra fire rate, damage, or health regeneration. In Vex’s case, skills can even be triggered through crit hits or minion deaths, opening the door for creative build paths that don’t rely solely on direct kills.
How Kill Skills Fit into Borderlands 4's Skill Trees
Borderlands 4 boasts the series' most ambitious skill system yet, with each of the four Vault Hunters—Vex, Harlowe, Rafa, and Amon—offering three trees packed with 20-25 skills per tree. To unlock deeper tiers, invest five points per row, gaining access to augments (modifiers for Action Skills) and capstones (powerful endgame abilities) after 15 points in a branch. Kill Skills typically appear in mid-to-late tiers, often as "Kill Skill" labeled passives that proc on enemy deaths.
For instance, Vex's trees heavily feature them, but they appear across classes. Here's a breakdown of key examples from recent build guides:
| Vault Hunter | Skill Tree | Example Kill Skill | Effect | Best For |
|---|---|---|---|---|
| Vex (Siren) | Vexcalation | Mortal Terror | Critical hits build stacks for fire rate and damage boosts, even without kills on weaker foes. | Single-target DPS and boss melting; synergizes with spectral blasts. |
| Vex (Siren) | Here Comes Trouble | Unsealed | Killing marked enemies grants her minion Trouble health regen and damage stacks; doubles during Phase Phamiliar Action Skill. | Minion-focused builds; great for mobbing adds in co-op. |
| Vex (Siren) | Dead Ringer | Overspirited | Kills with Ordnance or Action Skills spawn cryo explosive remnants. | Area control and elemental combos; pairs with phase clones. |
| Harlowe (Gravitar) | Cosmic Brilliance | Radiation Hazard | Killing irradiated enemies leaves damaging zones; refunds Action Skill cooldown on certain kills. | Radiation and entanglement playstyles; excels in crowd control on Kairos' factions. |
| Rafa (Brawler) | Arc Knives | Grave Assault (via shared perks) | Post-kill fire rate surge for slashing weapons. | Melee and knife-throwing builds; high mobility with dashes. |
| Amon (Engineer) | Overdrive | Volatile Hull Capstone Tie-In | Kills during cannon overdrive turn projectiles explosive. | Turret and heavy firepower; tanky setups against bosses like Vile Lictor. |
Vex stands out as the "kill skill queen," with trees allowing procs via crits rather than strict deaths, making her ideal for players who hate waiting for adds.
How to create a Vex Kill Skill build step by step
Vex's versatility makes her a prime choice for Kill Skill experimentation. Follow this detailed guide for your own Vex Kill Skill build:
Step 1: Choose Your Starting Tree and Action Skill
Select the Vexcalation tree for pure Kill Skill mastery, equipping the Incarnate Action Skill. This fires spectral blasts and boosts kill procs. At level 1, prioritize early passives like Grave Power to increase max stacks for all Kill Skills—aim for 3 points here by level 10. If you prefer minions, swap to Here Comes Trouble and summon Trouble the cat companion, which respawns on cooldown after kills.
Step 2: Allocate Points for Core Synergies
By level 15, invest in Mortal Terror (Vexcalation) for crit-based stacking— no need for full kills if you're landing headshots. Add points to Bloodletter passive, which applies bleed on crits (counting as gun damage). For augments, unlock Target Prescience to spike crit chance, feeding into infinite loops.
In Dead Ringer, grab Sanguine Fiends for minion health on kills and Diener for extra phase clone charges (up to 4 total). Use the in-game planner to simulate; class mods can grant bonus points, noted in skill descriptions.
Step 3: Gear Up for Procs and Sustain
Hunt for weapons with high pellet output, like Maliwan SMGs from pre-order bonuses, to maximize crits.
Equip Firmware mods that enhance elemental attunement (Vex converts skills to her gun's type). For the broken infinite damage setup discovered last week: Pair Bloodletter with a specific throwing knife (e.g., from Rafa's arc tree crossover) that refunds on bleeds. This loops damage endlessly, killing bosses in seconds even on True Vault Hunter mode (more on this at the end). Filter loot by rarity, damage type (e.g., Cryo for remnants), and manufacturer in the inventory for efficiency.
Step 4: Test in Combat and Adjust for Bosses
Drop into Kairos' regions for practice—use augments like Violent Outburst to sacrifice minion HP for manual kill procs during solo boss fights.
In co-op, coordinate with friends via the improved lobby for drop-in scaling. If stacks drop, respec at any New-U station (free post-level 20). Patch notes from September 16 indicate no nerfs yet, but Gearbox's creative director promises measured responses to exploits.
For other classes, adapt similarly: Harlowe's tree ties kills to radiation hazards for zone control, while Amon's overdrive builds explode on procs. Always check SHiFT codes for bonus points, with six active as of September 16, 2025.
Read: [Update: 16 Sept] All '6' Active SHiFT Codes for Borderlands 4
Vex's Infinite Damage Build
Recently, the community discovered a game-breaking infinite damage build using Vex's Kill Skills. By chaining Bloodletter bleeds with a knife with a Penetrator Augment, players one-shot endgame bosses, sparking debates on Reddit and X about potential nerfs. If you play with Vex, you wouldn't want to miss that.
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