By +16 repeating_crossbow.
This build is an alternative to the existing build that makes use of items from Blackmoon Keep obtained during haloween event and 2-3 extra talent points.
The kill chance is pretty abysmal but the lifesteal upgrade after you complete the relevant quest from first clear (not sure which boss) makes subsequent clears and also Blackmoon Keep (Upper) clears a piece of cake.
Lvl 50 or 1-2 extra talents would probably make the kill significantly easier. The talent points would go into feedback if you have them.
For this build I have all of the glory upgrades costing 20k and under, all of the available combat upgrades, 269 armory items, and 2172 gains levels. My stats might be slightly inflated from when I first beat it since I have gotten a few more armory items.
There might be ways to improve the build but this is what I came up with. For example, it was recommended below to swap the Taste For Blood (the weaker crit chance talents in the assassin tree) for Hidden Skills (the 1% attack speed talents in the assassin tree).
Click to enlarge…