Secondary Shiver greatly boosts damage against enemies affected by your spores. These funky infested pistols are pretty accurate, so you can reliably go for headshots on cold-affected enemies. A good Blast proc on a headshot will wipe out a bunch of enemies around your target as they all get affected by your spores.

Use [Magnetic Might] (not on this site yet) or [Galvanized Crosshairs] in the empty slot. I recommend using this mod instead of a Magnetic progenitor since it has some additional crit damage, to help scale our damage more as Acuity pushes us into higher crit tiers. If you have a lot of external fire rate (Arcane Velocity, [Reinforced Bond], [Wisp] motes etc.), replace [Anemic Agility] with the other. Same principle goes the other way if you have a bunch of external crit chance (Arcane Hot Shot, Avenger, Topaz Shards)
Secondary Deadhead is a good alternative to Secondary Shiver if you don't have it. Shiver has a higher ceiling for damage but less utility stats (-recoil and headshot mult)
Progenitor can really be anything you want, I like Cold/Heat to increase the Blast bias. Electric is good if using maxed Secondary Deadhead since its procs can be boosted by headshot multipliers. Magnetic is best if you're not using [Magnetic Might]