Condition Scourge
A Trailblazer's condition Scourge: Scepter/Torch pressure, 
Torment that burns, and a body the enemy struggles to remove from the line.
Where the power Scourge shields the squad, this one survives and keeps ticking. It wants a long fight against a group whose cleanse eventually runs dry.
Why these traits
The Scourge line is a burn engine: 
Demonic Lore makes your Torment hit harder and set the target on fire, 
Sadistic Searing adds burning to 
Nefarious Favor so the shade skill that cleanses your allies also cooks the enemy, and 
Fell Beacon both raises burning damage and converts your condition damage into expertise — that is where your duration comes from. 
Path of Corruption loads that same button a third time: Nefarious Favor is shroud skill 2, so pressing it now also converts two of the enemy's boons into conditions. That is the backbone of this build's strip; 
Well of Corruption, 
Trail of Anguish and 
Ghastly Breach corrupt on top of it. 
Insidious Disruption turns every disable into Torment, and you have plenty: 
Garish Pillar fears, 
Oppressive Collapse knocks down. Death Magic is what keeps you standing, but not the way you might read it: 
Putrid Defense grants carapace whenever you apply poison, 
Deadly Strength turns those stacks into power and condition damage, and 
Beyond the Veil cuts incoming condition damage once you are stacked — 
Death Nova only makes a poison nova when you or a minion goes down, and is not doing the work.
Gear reasoning
Full Trailblazer's with 
Trapper — toughness and vitality alongside the condition damage and duration, which is the whole plan: you are not winning a burst trade, you are still standing when the cleanse runs out. 
Demon Queen chains into the traits — a disable applies poison, that poison feeds Putrid Defense for carapace and cuts the target's healing on top. 
Corruption stacks condition damage off kills. Be aware that the two 
Torment sigils only fire on a critical hit and Trailblazer's buys no precision — 
Furious Demise and 
Target the Weak are the only crit chance you have, so those two slots are the softest part of the set.
When not to run it
Against a squad with disciplined cleanse, condition pressure evaporates and you can spend a whole fight contributing nothing. Take the power Scourge on the Scourge hub when you need damage that lands whatever the enemy is running.
It is also slow. Nothing here kills anything quickly, so if the fight is decided in the first push you will still be applying stacks when it is over.