History of Swashbuckler

Swashbuckler is a weapon trait: "This weapon gains increased damage from melee kills and kills with this weapon." Weapon kills grant one stack for 4.5 seconds (up to five, refreshing on gain), while a melee kill instantly grants all five. Bonus per stack: about 6% (d2 wiki: 6/12/18/24/30%) or 6.7% (light.gg-based: up to 33.3%). The sources disagree on the exact numbers, which may be version dependent.

It is notable on Heavy ammo weapons such as the Grenade Launcher Interference VI, the first grenade launcher able to roll it with Clown Cartridge. Compare Rampage, which needs several kills.