As a concept, Dark Justiciar mechanically does not work well in 5E. Like, yeah, you can slap-dash a vengeance paladin onto a trickster cleric and pretend it works, but it doesn't, not really.
The concept is "medium armored and martial armed zealot that is good at sneaking, illusion magic, phantasms, and combat". That is *a lot* of ground to cover. The entire thing COULD work as vengeance/oathbreaker paladin if the Dark Justiciar armors in the game weren't absolutely crap (Mail is a joke with the AC equivalent of light armor and pathetic extra damage on a 1- or 2-attack-per-round class; half-plate is decent, but you get it too late), and if they gave you access to some of the iconic abilities on the chest and helmet pieces...
In 3.5, you could maybe go with Divine Warrior (but alignment didn't fit), or Divine Seeker (but armor and weapon didn't fit), or any of the dozens of paladin variants...
