Built Bitter

Built Bitter is the 2-piece set bonus of the Deep Explorer armor set, which comes from the Duality dungeon. Taking damage increases the reload speed of your equipped weapon until you stow it, and taking more damage strengthens the effect.

The set's 4-piece bonus, Bittersweet, restores health when you stow a weapon, based on how many Built Bitter stacks you lost. The set bonuses also work in PvP as well as PvE.

You need four of the set's five pieces for the full bonus, which leaves one slot free for an exotic.