If you’re chasing some of the strongest legendary items in Borderlands 4, you can’t skip Leader Willem. This boss drops three powerful exclusives — Zipper (Pistol), Firepot (Grenade Mod), and Rainbow Vomit (Shotgun) — each with unique mechanics and enormous farming value. Below, you’ll find a complete breakdown of how to find Leader Willem, unlock the fight, and farm his best gear efficiently.
Where to Find Leader Willem & How to Unlock the Fight
Leader Willem resides beneath Carcadia Hub, inside the Grindstone of the Worthy zone, accessible through The Excrucible.
To unlock this encounter, complete the “Enter the Electi” questline from NPC Levaine in Carcadia. The final quest, “The Mole’s Gambit,” triggers the boss fight.
After defeating him once, you can refight Leader Willem endlessly using Moxxi’s Big Encore Machine, making this one of the most reliable Borderlands legendary farm routes available.
How to Battle Leader Willem
Leader Willem’s fight features two defense phases — Shield and Armor — so you’ll need to switch elements mid-fight:
● Shield Phase: Use Shock damage weapons to deplete his energy barrier quickly.
● Armor Phase: Switch to Corrosive damage for maximum armor penetration.
● Survival Tip: Keep moving, dodge projectiles, and leave one or two mobs alive to trigger Second Wind.
● Difficulty: Farm him on Easy Mode — dedicated drops are not affected by difficulty level.
Loot Overview
Leader Willem drops three exclusive legendary items:
● Zipper — Pistol
● Firepot — Grenade Mod
● Rainbow Vomit — Shotgun
It usually takes around 30–40 kills to collect all three. However, drop rates vary greatly between players. Below is a detailed breakdown of each weapon.
Zipper (Pistol)
Manufacturer: Datalless
Flavor Text: “Prison rules.”
Effect: +75 % Critical Damage and +75 % Bonus Damage when attacking enemies from behind.
Base Stats:
DPS 3,240
Base Damage 835
Fire Rate 6.2 shots / s
Reload Time 1.5 s
Magazine Size 16
Although the description sounds powerful, it performs poorly in high-difficulty or boss fights. The weapon relies heavily on accurate back attacks — something hard to achieve against bosses. Unless you obtain an exceptionally rolled version, it’s not worth farming.
Firepot (Grenade Mod)
Type: Grenade Mod
Description: Spawns auto-tracking sticky explosives that deal Fire damage.
Base Stats:
Damage 6,850
Cooldown 11 s
Explosion Radius 520
Charges 2
Flavor Text: “Spicy spawns homing Torgue stickies over time.”
Mechanics:
● Stickies attach to enemies or surfaces and detonate automatically.
● You can swap weapons to trigger an instant detonation for burst damage.
● The Atomic / Nuke variant dramatically increases explosion size and power, ideal for clearing rooms or bursting down bosses.
Widely considered the best drop from Leader Willem, the Firepot is effective for every class and excels at both mob clearing and boss fights. It’s one of the most versatile grenade mods in Borderlands 4 — a top-priority farming target.
Rainbow Vomit (Shotgun)
Type: Torgue Shotgun
Flavor Text: “Color Spray.”
Effect: Fires three random elemental projectiles (such as Corrosive, Shock, Cryo, Fire, or Radiation).
Base Stats:
DPS 5,154
Base Damage 823 × 6
Reload Time 1.7 s
Fire Rate 1.5 shots / s
Magazine Size 6
The Spread Launcher variant delivers massive burst damage, especially with the Incendiary + Shock + Corrosive elemental combination that excels against all enemy types, and although its power drops off at long range, it remains devastating up close—just be prepared for a longer grind since its drop rate is significantly lower than the other two items.
