The unlockable for the Heaviest pugilists out there is the K.G.B. Any time a Heavy kills an enemy with the K.G.B he receives five seconds of guaranteed critical hits. This crit-boost can be used to punch and kill further enemies, extending the boost time. Alternatively, the Heavy can switch to another weapon and use the boost to take out an enemy at range. The Heavy's slow movement speed, and the K.G.B's slower swing speed, make it a risky prospect.