Test. Crit-based Synapse for a themed Nidus+Helminth endgame build.

Vital Sense is probably the best spot for your Riven/flex slot. Godroll for the Riven would be CC, CD, Punch, and whatever negative. If not, you can swap that out for a vital sense (as shown).

The Epidemic build can push crazy crit bonuses to your Primary. As is, that'd be 97.5%, plus the 225-250% boost from Teeming... golly. Something like 180% critical chance. WHICH IS AMAZING. Add in a CD+CC riven in place of your [Vital Sense], and suddenly your crit chance is hitting like 250+% crit. That's amazing.

AMAZING!