What to know

  • The Vex infinite damage build centers around the Vivisecting Throwing Knife with the Penetrator Augment that does heavy, crit damage.
  • Any purple Vivisecting Throwing Knife will do the trick, including Vampiric, Rapid, Augmented, Fully Loaded, Killshot, and Bullseye Vivisecting Throwing Knife.
  • Vex's Bloodletter and Contamination passive skills stack bleed status effects for rapid critical damage.
  • This combo melts bosses in seconds, even at high difficulty, and works with lower-level weapons.
  • This build is said to work only for solo players and may be patched quickly.

Take advantage of Borderlands 4’s game-breaking mechanics while they last. Players are talking about the Vex Siren build that dishes out infinite damage through clever passive stacking and weapon selection. Here are the exact steps and talents you need, the mechanics, and a practical solo boss strategy.

What Infinite damage with Vex consist of

Here are the main ingredients of the infinite damage hack:

Mix of a purple Vivisecting Throwing Knife and Critical Hits

The Vex infinite damage build exploits a special weapon—the Vampiric Vivisecting Throwing Knife with the Penetrator Augment. Basically, once a target is hit with this knife, every bit of damage dealt for the next five seconds becomes a guaranteed critical hit, including damage-over-time effects like bleed.

Although we mentioned the Vampiric Vivisecting Throwing Knife, there are a few of these purple throwing knives with Penetrator Augment going around (that will work). Other than the Vampiric, there's also Killshot, Rapid, Augmented, Fully Loaded, and Bullseye Vivisecting Throwing Knife.

Passive skills and feedback loop

Vex’s Bloodletter talent grants a chance for gun and skill critical hits to apply bleed, causing stacking kinetic damage as a status effect.

Contamination, her other key passive, pushes the chance for status effect application up to 100% when scoring critical hits. Together, these create a feedback loop: every crit applies bleed, and every bleed tick counts as a crit, which further triggers more bleeding—stacking exponential damage.

Weapon choices and gear flexibility

While theorycrafting usually encourages max-level gear, this build only needs the right augment and talents. The Vivisecting Throwing knives works regardless of its level, meaning a lower-level item is sufficient on a high-level Vault Hunter if the Penetrator Augment is present. Shotguns are recommended for increased base damage and smoother stacking, but anything with Kinetic harm fits.

Here's a quick breakdown of Equipment & Weapons:

  • Throwing Knife: A Vivisecting Throwing Knife with Penetrator Augment – Damage. This is essential.
  • Guns: Once the bleed+crit loop is working, almost any gun works. But for best results, high base damage + kinetic weapons are preferred (e.g. Jakobs shotguns. SMGs also good if you like faster rate).
  • Repkits / Augments: Look for damage amp % rep kits, action skill cooldown, status effect chance, etc.
  • Special gear/utility: Class mods that boost Bloodletter, critical hit damage, status effects, etc.

Step-by-step guide: How to achieve infinite damage with Vex

Here's how you can achieve infinite damage with Vex yourself:

Step 1: Get a Vivisecting Throwing Knife

Aim for one with the Penetrator Augment. Farm or buy until this specific combination appears—the knife’s level doesn’t matter if the augment is present (check the guide below about farming the Penetrator Knife below).

Step 2: Assign passive skills

Slot Bloodletter and Contamination in Vex’s skill tree. Max out Bloodletter for frequent bleed procs and Contamination for maximum status application.

Step 3: Prepare a high base damage kinetic weapon

Optionally pair the knife with a strong shotgun, preferably Jakobs for synergy, or any high-damage kinetic gun. This boosts stacking bleed values.

Step 4: Execute the setup on a boss

Throw the knife to apply Penetrator Augment; follow up immediately with a critical hit from your weapon. Watch as the bleed statuses begin stacking rapidly and the boss’s health plummets in seconds.

Step 5: Repeat for farming

Use this strategy for quick legendary drops and rapid solo boss farming. Note: this build does not currently work in multiplayer due to a bug.

How to Farm the Penetrator Knife

Securing the Vivisecting Throwing Knife with Penetrator Augment is crucial, as it's a rare drop. Focus on endgame farming spots post-campaign.

Step 1: Reach Endgame Content

Complete the main story to unlock Ultimate Vault Hunter ranks. This build performs best at rank 5, but test it earlier on normal difficulties.

Step 2: Target High-Yield Areas

Head to Splashzone, a repeated boss arena ideal for legendaries.

Run the Primordial Guardian Inceptus encounter—its loot pool includes knives. Equip loot filters for throwing ordnance.

Driller Hole near Carcadia is another boss that drops a lot of good gear. Easy to kill and farm for loot.

One final boss to farm loot (and potentially the Penetrator Knife) is the Rippa Roadbirds in Saw's Clench.

Step 3: Optimize Your Run

Use fast-travel and skip mechanics if available. Pair with a temporary minion build (e.g., Dead Ringer from The Fourth Seal) to clear adds quickly. Expect 20-50 runs; drop rates hover around 1-2% based on community reports.

Step 4: Augment and Test

Once dropped, apply the Penetrator Augment at a blacksmith station. Test on low-threat enemies to confirm the crit loop before bosses.

While devastating, this build isn't flawless. Co-op glitches aside, it demands precise knife throws, and stability issues like UI freezes have cropped up in tests. Gearbox's creative director has acknowledged Vex's bleed potency, hinting at investigations into crashes. With the game fresh from launch, expect a hotfix. So try the infinite damage trick ASAP.