Updated build for 30.5 -
Since pure damage scaling isn't as efficient now with the introduction of secondary arcanes, [Hornet Strike] cane be substituted out in favour of bonus faction damage, this is to double dip the slash procs provided by [Hemorrhage].

Alternate substitute mods in place of primed expel {faction} can be base [Hornet Strike] if you chose not to swap out the mod between missions, [Sharpened Bullets] or [Seeker]. Primed expel {faction} has a significant damage boost however once the galvanized mods and the arcane are stacked.

Riven Suggestions
There are only 2 stats you want to look for in a Zymos riven although its base stats aren't crit heavy - its crit stat multipliers are the best of any weapon in the game. So the ideal riven roll would be +CC +CD -Harmless. With the current riven disposition as of writing this guide, a double crit riven would give you over 130% CC with roughly x20 CD with larva on headshot.

At full galvanized/arcane stacks, expect the [Zymos] to require 1 headshots to kill a 185 heavy gunner (Due to AoE nature of larvam this can also extent to large groups of enemies). All builds and mods suggested were tested in both simulacrum conditions vs lvl 185 (Grineer Heavys, Corrupted Heavy, Grineer Bombard, Corrupted Bombard) followed by 1Hr SP Mot runs.