Here is a quick concept around merc unique belt - Binds of Bloody Vengeance, ability to self crit through various means(I forgot to mention Enmity's Embrace as a 100% trigger which is a bummer).

In short: we self reflect Brittle to apply flat crit chance to the character, then do a self hit in order to crit, so we have a 100% crit and build around it. Raw skeleton I made for t16 testing out of pconc elementalist: https://pobb.in/RsHhdWB0QPxV