Note: Gladiator Might can be used instead of Drifting Contact, but it requires Primary, and/or Secondary Dexterity to give you more time before the Combo Counter resets. Can also use Naramon to make it go down by 5, instead of full resetting.

This build, with a Primed Smite mod, focuses on pure Slash damage. It requires a primer, of some sort, so that Condition Overload works better than Primed Pressure Point; if you don't want to use a primed, then use the Primed Pressure Point instead.
For a Viral + Slash build, you can replace Weeping Wounds and the Primed Smite mod for the Viral 60/60 mods (Vicious Frost, and Virulent Scourge).

Alternative Heavy build ([Quassus] only): [Primed Pressure Point], [Sacrificial Steel], Killing Blow, Amalgam Organ Shatter, North Wind, Primed Fever Strike, Berserker Fury, Corrupt Charge.
Note: You can use the Viral 60/60 mods (or just one of them), and a Primed Smite mod, but that would require you to either build up Combo Counter (replacing [Corrupt Charge]), or have another source of Attack Speed (replacing [Berserker Fury]).

Warfan Stances: [Votive Onslaught].
Note: Do not use the other Stance mod, unless you're using your Warfan as a stat stick, or with a Heavy build.