1-4% to Instakill human-sized enemies on Chained Heavy Hit. Stacks 5 times. Note that other potential triggers will not be activated on Instakill.
4.5-6% Strength on Repeated Weak Spot Hit. Stacks 5 times.
0.45-0.6% Critical Chance for each expended round in your weapon (resets on reload).
10% Critical Chance for every 0.2-0.35 second while aiming. Stacks 10 times. Discharges all stacks upon firing.
Knife lets you chew up hordes and deal stupid amounts of damge on melee headshots to basically anything. Stealth to get out of bad situations or get a res, or to get a bunch of extra damage on ranged headshots. Finish stuff off with the punch for funni.