The Throwing Knife with the Penetrator augment—often called the “crit knife”—is currently one of the strongest single-target tools in Borderlands 4. Tagging an enemy applies a brief debuff that turns all incoming damage into critical hits, letting even modest builds melt bosses during that window. The catch: it’s a purple world-drop, so there’s no dedicated loot pool. Here’s how players are reliably securing it and looping fast runs.

Penetrator augment: what it does and why it’s meta

When a target is hit by a Throwing Knife that rolled the Penetrator augment, all damage dealt to that target becomes guaranteed critical hits for five seconds. That short window is the entire playstyle—apply the knife, then dump your highest-output skills and weapons while the debuff is active.

  • Timing matters. Throw the knife first to “prime” the enemy, then activate your Action Skill and damage buffs.
  • It stacks with class and gear multipliers. The crit conversion amplifies any strong burst setup you already have.
  • It’s single-target. Great for bosses and elites; less impactful for wide mobbing without additional crowd tools.
Note: Players are also reporting interactions that push damage into extreme territory, sometimes deleting bosses in a single cycle. Balance changes could shift the exact numbers, but the core five-second crit window is what makes Penetrator so valuable.

Best farm: Driller Hole (Queen’s Cradle, Tonnage Peel, Carcadia Burn)

The most consistent community farm for Throwing Knives, including Penetrator rolls, is the boss Driller Hole. The fight is short, drops plenty of Ordnance (the item family Throwing Knives belong to), and opens a Red Chest in the reward room after the kill—another high-velocity pull of purple loot.

  • Access: Driller Hole is available after the main mission “Unpaid Tab.”
  • Damage types: Driller Hole spawns with Armor followed by Flesh. Bring Corrosive or Cryo to pop Armor quickly, then Incendiary to finish.
  • Loop: Kill Driller Hole, then head through the southeast door that opens to the Red Chest. Repeat the encounter for more rolls.

Because Penetrator is not a dedicated drop, you’re targeting speed and loot volume. Driller Hole offers both, which is why it’s the current go-to even though any source can roll the knife.

Encore Machines: fast boss resets and a weekly “Big Encore”

Encore Machines let you refight bosses on demand, removing travel friction from farm loops. Activating an Encore costs currency that scales with your level, but the time saved makes it the most efficient method to stack attempts.

  • Use Encore for Driller Hole loops to chain kills and Red Chest openings with minimal downtime.
  • Weekly Big Encore: A harder, 100 Eridium variant that drops more loot. It unlocks after finishing the main story and enabling Ultimate Vault Hunter Mode.
  • Spend Eridium only if you want the extra-chunky loot bursts; standard Encore farming remains efficient for Penetrator rolls.
Tip: If you’re early in the game, the standard Encore Machine path is your best bet. Save Eridium for Big Encore once you’re settled into endgame.

Yes, it’s a world drop—what that means for your farm

The Penetrator Throwing Knife is a purple-rarity item that can drop from virtually anywhere: bosses, Badass enemies, standard chests, and activity rewards. That’s good news for availability but bad news for targeting a specific augment.

  • Early-game loop: Even early bosses can drop it. Some players grind the first boss encounters for quick clears, but yield for Throwing Knives varies by spot.
  • Activity farming: Content that pays out lots of chests and elites—like drill sites or vault-style arenas—can roll Throwing Knives in bulk. It’s less focused than a boss loop but still viable.
  • Why Driller Hole wins: Short fight, reliable Ordnance drops, and a Red Chest in the same run.

How to use the crit window effectively

The augment is only as strong as your five-second burst. Structure your inputs so every heavy multiplier lands inside the window.

  • Apply Penetrator first. If the knife doesn’t tag the target, you won’t convert damage to crits.
  • Queue your burst. Activate Action Skill, fire off high-impact shots, then reload or swap as the window ends.
  • Refresh if needed. If the target survives, reapply Penetrator and repeat the sequence.

Because all incoming damage becomes critical, weapons or skills with big base hits shine. Sustain tools matter less than clean execution during the debuff.

What to look for when a knife drops

Don’t overthink rolls at first—your main goal is simply securing the Penetrator augment. Once you have it, you can get picky.

  • Must-have: The Penetrator augment on a Throwing Knife.
  • Nice-to-have: Bonuses that amplify burst (e.g., class synergies, damage buffs) during the five-second window.
  • Optional extras: There are other effects in the game that interact with critical hits. They can stack into powerful boss phases when timed with Penetrator.
Farm method Why it’s good for Penetrator Requirements Key notes
Driller Hole boss (Queen’s Cradle) Fast fight, strong Ordnance drops, extra Red Chest Unlock via “Unpaid Tab” mission Bring Corrosive/Cryo for Armor, Incendiary for Flesh
Encore Machine loops Instant boss resets to stack attempts quickly Encore currency (cost scales with level) Best way to minimize travel and loading
Weekly Big Encore Increased loot volume per clear 100 Eridium, story complete, UVHM enabled Harder variant; efficient if you want bulk rolls
Early-game boss spam Very fast resets on low-HP bosses None World-drop RNG; yields vary widely
World activities and chests Lots of chances at purple drops None Unfocused but synergizes with general farming

Common pitfalls and quick fixes

  • No crits after tagging: Make sure the knife actually connected; rethrow if you whiff the target.
  • Buffs missing the window: Activate your Action Skill right after the knife lands to maximize the five seconds.
  • Slow runs: Use Encore Machines to eliminate backtracking and spend your time on kills, not travel.

If you’re chasing the crit knife, prioritize speed over destination: short boss clears, instant resets, repeatable chests. Driller Hole hits that balance today, and Encore Machines do the heavy lifting for quick loops. Once you land a Penetrator roll, build around the five-second crit window—and watch bosses evaporate.