Huntress
Amazonall of your single target damage depends on 
High Velocity Rounds hitting hard (due to Riven Armor storing 5% of its damage), therefore, the goal is to make its damage as consistent as possible.
focus on getting a crossbow with as much Accuracy as possible (due to Amazon's 
Penetrate), which adds to both your min AND max dmg values simultaneously, making the "spread" of High Velocity Rounds as low as possible.
then, you want Garukhan's Resolve ASAP, as it essentially rolls your crit chance twice (already good) AND gives the chance to double your crit damage.
SINGLE TARGET
stand as CLOSE AS POSSIBLE to the enemy for maximum dps!
Despair (time it right before the boss spawns due to delay)
if you have
Escalating Mayhem, also do a few 
Spearfields here
War Banner -
Armour Piercing Rounds until armor is Fully Broken - High Velocity Rounds to apply Riven Armor debuff (ensure you are moving for
Spray and Pray) - Spearfield spam until Riven Armor expires, then go back to Step 2
due to Riven Armor's dmg being UNSCALABLE, the actual damage Spearfield does is ENTIRELY IRRELEVANT - we just attack as fast as possible to generate poisons with 
Splinter of Loratta
also, if you REALLY want to min-max, you can also toss in a 
Crossbow Shot directly before using High Velocity Rounds to get a bit more dmg due to Impale. don't feel like you HAVE TO do this, though.
CLEARING
just 
Siege Cascade all over the place (
Herald of Blood + 
Herald of Plague clears everything)
