This is a hybrid primary/secondary fire Bubonico build, using the alt-fire to both prime enemies with viral + electric status, create AOE electric DoT that chains and kills weaker enemies and switching to primary fire to finish off heavier units with both up front corrosive damage and slash procs.

Electric/Corrosive
The key element is electric from Primed Charged Shelll, which combines with toxin on primary fire to make corrosive damage, which is effective against Ferrite armor commonly seen on Grineer, Acolytes and Infested, and adds electric to the viral damage on secondary fire. This ultimately gives Galvanized Savvy up to 6 different elements split between primary and alt-fire.

When combined with a grouping ability such as Nidus Larva, Khora's ensnare or Vauban's vortex, the electric procs from the alt-fire create tons of chaining arcs of electricity whch deals massive damage to a group. Any heavily armored enemies that survive the electical storm onslaught can be easily finished off by primary fire's high crit chance projectiles that proc slash from hunter munitions, which is boosted by the viral procs created by the secondary fire.

If you prefer to only use alt-fire to nuke trash mobs, replace Galvanized Savvy with primed point blank, critical deceleration with shell shock and primed ravage with primed ammo stock

Cold/Viral
Adding Chilling Reload or Frigid Blast over Primed Charged Shell slot creates viral on the primary fire and adds cold on the alt-fire. (note Primed Chilling Grasp would NOT fit unless you change the innate - polarity to a D). Cold on the alt-fire allows you to slow enemies by up to 80%, applying even through Overguard, as well as boosting crit damage by a final additive +0.5.

If you are using ARMOR STRIP, swap Hunter Munitions for Primed Point Blank and Primed Charged Shell for Chilling Reload/Frigid Blast.

Pure Toxin
An anti-corpus version uses pure toxin on both primary and altfire to bypass shields, simply replace Primed Charged Shell with Contagious Spread.
See anti-corpus version: https://overframe.gg/build/217932/bubonico/bubonico-anti-corpus/

Here is a brief rundown of the mods:

• Galvanized Hell : Gives up to +230% multishot
• Galvanized Savvy: Adds 80% extra status chance, good for alt-fire, and increases damage of primary fire based on amount of status procs - giving up to +80% damage for each status. Since alt-fire has such high status, all enemies will be afflicted with viral and electricity equating to +160% extra damage. After a few shots of primary fire, it will likely proc IPS + corrosive, giving a maximum damage bonus of +480% damage at 6 statuses. Note that as of writing this (Update 30.7), [Galvanized Savvy] damage bonus does NOT apply to secondary fire AOE, but does apply to the primary fire, and is infact multipicative to primary merciless (i.e. +480% x +360% = +2500% damage).
• Critical Deceleration : +200% crit chance, much greater than that offered by blunderbuss, but at the cost of fire rate
• Shotgun Barrage: to offset the fire rate penalty from critical deceleration and increase DPS
• Primed Ravage : Critical damage
• Hunter munitions : Creates slash procs that bypass armor
• [Primed Cleanse Grineer]: Double dips on slash and electric procs by increasing base damage and DoT proc amount. Use regular Cleanse Grineer if no primed version. Can swap out for cleanse corrupted or infested if required depending on faction.
• [Primed Charged Shell] : gives high raw corrosive damage for primary fire and electric procs for secondary fire. Use [Shell Shock] if no [Primed Charged Shell].

Flexible Options
You can replace any of the above mods if you dont own them or prefer not to run them with the following:

• Primed Point Blank - multiplicative with galv savvy but additive to arcane, can slot over faction mod if you DON'T own Primed Cleanse version or if you just prefer not to run faction mods.
• Primed Ammo Stock - improves quality of life as you can dump more magazine before needing to recharge
• Primed Tactical Pump/Seeking Fury - improves quality of life and reload increases recharge speed

Arcane
Primary Merciless: Triggers from slash proc kills and boosts reload slightly as well as providing +360% dmg which is multiplicative to Galv Savvy

Primary Frostbite and Blight are NOT worth using on Bubonico because the +dmg from merciless/deadhead is multiplicative to Galv Savvy.

Riven
Slot over Shogun Barrage slot if possible:
Best Positives: +Crit Damage, +Crit Chance, +Multishot, +Fire Rate
Decent Positives: +Damage, +Magazine Capacity, +Reload

Here's an example showing Nidus with Teeming Virulence, firing alt-fire into a Larva which nukes most enemies with electric status, then primary fire hits for orange and red crits, killing remaining enemies and acolyte quickly: