There are Required combo setups in this [Synapse] build to increase its potential.

(Optional) Arcane [Rage]: Well you are going to hit some headshots with that [Galvanized Scope] so might as well add more Damage ;)
(Optional) Arcane Avenger: Flat 45% Crit rate (Well more REDS to see) I have the [Combat Discipline] Aura in my warframe ([Revenant]) and also the Subsumed Gloom of [Sevagoth] for the lifesteal. So this will have a infinite cycle of damage taken and lifesteal to keep the Arcane Avenger buff up.

(REQUIRED) [Panzer Vulpaphyla]: Very awesome pet and probably the most important one in this combo as its spreads viral for the Viral+slash Meta So that's why you can't see a viral element in the weapon.
Just wait for the Vulpaphyla to spread its viral and fire away and see them melt!

You can also change the Riven mod for a [Vital Sense] if you don't have any rivens.

As for the Exilus you can add the vigilante mod but it'll require 1 more forma.