What to know

  • Throwing knives replace grenades as "Ordnance" items, dealing direct-hit damage and applying powerful augments like guaranteed crits.
  • The "crit knife" refers to variants like the Vampiric Vivisecting Throwing Knife with Penetrator Augment, forcing all enemy damage to crit for 5 seconds.
  • It enables infinite damage loops with Vex's bleed skills, melting bosses in seconds—though Gearbox may nerf it soon.
  • Farm them via bosses like Splashzone or Encore Machines for the best drop rates on this game-changer.

Nicknamed the "crit knife" by the community, the throwing knife in Borderlands 4 is more than your standard melee tool. It's a throwable Ordnance weapon that can supercharge your damage output.

When this knife hits an enemy, all subsequent damage to that target becomes critical hits for 5 seconds, greatly increasing damage output. This mechanic effectively enables players to melt bosses and enemies by stacking critical hits from guns, skills, or damage-over-time effects while the crit effect is active. Basically, you can achieve infinite damage loops that can decimate the biggest bosses in seconds.

How the crit knife build works in BL4

This throwing knife is especially valuable in builds that utilize critical hit synergies and bleed effects, such as Vex’s bleed build, where critical hits also trigger bleed status effects that loop and cause massive damage escalation. Here's how it works.

Mechanics behind the loop

Penetrator augment on the throwing knife

When you hit an enemy with this knife, that enemy gets a temporary effect which makes all damage dealt to them count as critical hits for a short duration (≈ 5 seconds).

Bloodletter passive (Vex)

Allows critical hits / skills / guns to apply bleed status effect. Bleed causes damage over time in ticks.

Contamination passive (Vex)

This increases the chance that status effects are applied, especially after critical hits, pushing that status application chance near or up to 100%. So each bleed tick (counted as a crit thanks to Penetrator) reliably applies bleed again.

Why the crit knife powers up Vex builds

Vex turns this knife into a boss-slaying machine through her Vexcalation tree. Bloodletter passive gives crits a shot at applying bleed DoT, but the knife forces those bleeds to crit too—each tick ramps damage kinetically.

Vexcalation tree (focus on Bloodletting and Contamination)

Layer on Contamination, which caps status application at 100% from crits, and bleeds chain infinitely. That exponential stacking is what allows very large damage in very short time, effectively “infinite” damage until the boss is dead or you can’t keep applying.

How to build the crit knife (with infinite damage) Vex build

Here’s a step-by-step guide to get this working in your gameplay.

Step 1: Acquire the right throwing knife
  • Look for a Vivisecting Throwing Knife with the Penetrator — Damage augment. There are variants (Vampiric, Rapid, Fully Loaded, etc.) that may also work as long as the Penetrator Augment is present.
  • It’s purple rarity, and drops are rare. Farming bosses via Encore Machines is among the more reliable methods. Also check loot from weekly big Encore Boss, stronger bosses, chests, etc.
Step 2: Spec your character (Vex)
Via X
  • Put skill points into Bloodletter to enable bleed proc from crits.
  • Also invest in Contamination to raise status application chances post-crit.
  • You may want supplementary passives or gear that boost crit damage, bleed damage, status effect duration, etc.
Step 3: Select gear & weapons to complement
Via X
  • Although the knife handles the core mechanic, pairing with high base-damage weapons helps (for follow-up shots, etc.). Kinetic damage weapons are often preferred.
  • Gear that boosts survivability or boosts status / crit damage helps make the loop more sustainable.
Step 4: Execute in combat
  • Throw the knife to hit a target and activate the Penetrator effect.
  • Immediately follow up with critical damage / bleed-applying shots (or skills).
  • Keep attacking / triggering bleed ticks so status stack continues.
Step 5: Use for farming or boss fights
  • Boss fights are where this build shines. Big bosses may have huge health pools, but once the crit damage loop is running, they melt fast.
  • For farming the knife, focus on bosses or high-reward activities. Splashzone is one location flagged by the community as good for finding the needed knife.

Limitations, risks, and what to expect

Limitation / Risk Details
Co-op limitations Reports suggest that if more than one player uses the same crit knife / build in the same fight, the effect may not stack properly or may glitch. The loop may break.
Durability and timing Penetrator augment lasts only ~5 seconds after a knife hit. If you miss, delay, or get interrupted, you lose the effect. Bleed ticks need to keep applying.
Gear drop rate and RNG Getting the exact throwing knife with Penetrator augment is rare; RNG plays a large role. Might require many farming runs.
Potential for nerfs Since the build is overpowered and trivializes many encounters, the developers are likely to adjust balance in future patches.

The “Crit Knife” build in Borderlands 4 (the Vivisecting Throwing Knife + Penetrator augment + Vex’s bleed & status passives) is currently one of the most powerful exploits in the game. It unlocks a damage feedback loop that turns bleed ticks into crits, and crits into more bleed, rapidly demolishing enemies — especially bosses.

If aiming for speed, loot farming, or clearing endgame content, this build is extremely effective right now. It’s likely to be adjusted in future updates, so making the most of it while you can is advisable.