Sitting here trying to sift through and organize the vast amounts of equipment I have and just found this.
Bloodthirst Dagger mainhand
Knife of UnderMountain King Shortsword offhand
The Dead Shot Bow (could give this bow to a mele and it Improved Crital does work on mele strikes.
Sarevok's Horned Helmet
Works for the dagger and bow hits.
I just kept shooting to see if 16 would crit, as I was not sure if the Undermountain King would react differently saying it crits upon 19 instead of 1 less, but I just critted on a 16 roll.
Champion sub on Warrior would drop it down to 15.
Pretty nifty. Especially with Advantage which gives you two dice rolls.
Not the most broken thing in the game and takes up you helm slot and a shield use(could) make the case you'd be using the weapon set regardless), but pretty cool.