The Exergise is a great Status Ailment Shotgun, able to [Reach] 100% status chance per pellet with just the three essential Status Chance mods for getting Heat and Viral onto the weapon. For those not familiar with why this is important, heres a quick breakdown:

• With 100% status per projectile, each one of the pelets from this gun will inflict a status ailment. Which one is determined using the percentage of each damage type. For example: a pellet deals 100 damage - 25 of that is slash, 35 is Impact and 40 is viral. When that pellet deals a status ailment, there is a 25% chance its slash, 35% chance it is Impact and 40% for a viral status ailment.
• Viral status ailments increases all damage that enemy recieves to its health. It's first proc increases it by 100% (total of 2x damage to health) then each consecutive one adds 25% up to 10 stacks. This means a status gun should really aim at having this be its highest damage number only slightly ahead of slash so it can reliably get a few of these inflicted
• Slash status ailments deal true damage based on how much slash damage your weapon has. This bipasses armor AND is increased by your Viral procs, meaning it can melt through an enemy with even high armor by going straight for their health.
• Heat status ailment removes 50% of an enemies armor and does heat damage over time. That armor shred effect does not increase with more procs, so we only want it to reliably proc once so our non-status based damage still hits hard.

This weapon will easily chew through the Steel Path. A strong synergy is to use Ripkas with their unique mod Amalgam Ripkas True Steel. It gives free reload speed which is extremely useful and as a fun bonus will make your Nekros very happy as guaranteed Gore chances means double the drops for him (yes this is a real mechanic)

Alternative Builld - Does require different polarizations!

If you don't love using two shots on a weapon that flavor wise is only supposed to shoot one, try these alterations:

• Replace [Galvanized Savvy] with Vigilante Armaments
• Replace Ammo Stock with Vicious Spread
• Replace Primed Chilling Grasp with frigid blast

This preserves the "1-shot of death" feel of the normal gun though it does rely on its slash damage to really get through enemies. Still suitable for litterally all content in this game besides maybe later Steel Path Enemies.