1-4 Bleed Stacks on non-Weak Spot Hits.
70-100% Rending on Backstab Hit.
This build focuses on proc-ing crit strikes with bleed and thereby bleeding from crits. Each crit will give you toughness damage reduction as well as cooldown reduction on your shroud field. Successful dodges also increase your toughness damage reduction and movement speed. Put that all together and you will be very tough to kill in melee.
Since this is a dagger build you will need to focus more on avoiding being hit with dodges and Shroudfield. Shroudfield will be key for this build. With increased duration to 6 seconds and 1.5s cooldown reduction on crits you will be able to keep a near 50% uptime on Shroudfield if needed. This allows you to carry the team very easily if two or more allies go down. You can Shroudfield, pick an ally up, then quickly proc crits to reset your cooldown. If your entire team dies you can sprint/shroudfield past hordes of foes and easily pick up the clutch.
You can use your speed and stealth to pick off threats to your team before they become a problem. Make sure to focus on heavy backstabs for any non-poxwalker enemies. With the boosted backstab damage from the skill tree and ruthless backstab on the dagger you will be able to 1-2 tap a crusher with a heavy backstab from Shroudfield.
Since the throwing dagger gets bonuses from your held weapon, while you have high crit chance proc-ed, you will be able to one shot most specials (trapper, mutant with a weak spot hit, hounds, flamers, snipers, rager). Make sure to refresh your throwing knife charges by killing specials in melee.
Note: You can swap "Duelist" for "Good ballance/Ambuscade" if you need more damage mitigation at the cost of backstab damage. I find I don't take enough damage for this to be worth the tradeoff.