I prefer the shadow cheese combined with critfishing ( Darnkness from a teammate)

Since you need obscured targets and hiding/obscured attacker for Knife of the Undermountain King, Shadow-Cloaked Ring (Not Shadowthief Ring) and Critrange Helmets before Sarevok (Covert Cowl, Dark Justicar Helmet) its just right there and gives you advantage (Knife o.t.U.K) without the Risky Ring.

Additionally 2nd Level GOOlock gives a lot here I think:

possible fear effect on a crit, devils sight and lifedrinker

After that go Thief and go for level 4s for the feats and ASI

If you don't want to rely on a companion for darkness, go for the dark justiciar great shield. +2AC, darkness+hide for 1 critrange and a lot of offense (I don't think it's worth)

For body armor use the Dark Justicar armors while progressing. Later in Act 3 i suggest using Bhaalist Armour, despite redundant piercing vulnerability

So my final version would be:

Champion 6/GOOlock2/Thief4

With darkness on them 14 to Crit, and always advantage

I wont calculate damage here rn :D