After about a year off and on of farming Vodyanoi I thought I'd offer some wisdom for how best to use Nekros in an Endo farming group.

Mods

• Corrosive Projection: You should NOT be focusing on ANY OTHER damage type other than SLASH or COLD while killing Executioners, which makes Corrosive Projection better than Steel Charge as an aura, even if you're solely using a melee weapon.
• Thief's Wit: Since you're here to farm Endo, being able to locate it when it commonly pops up across the map will get you a bit extra in most rounds.
• Fleeting Expertise and Overextended: Only range and efficiency are needed for [Nekros] in Vodyanoi, everything else should focus on survivability for Steel Path. The maximum efficiency of 175% isn't critical with [Despoil] and a [Wisp] in the group constantly healing you with a Heal Mote, and maximum range is also a waste because the whole group is clustered together in one spot. Therefore, just these two mods are necessary to take care of efficiency and range. Stretch is also a viable alternative and has plenty of range by itself.
• Health Conversion, [Adaptation], [Vitality], Carnis Carapace: Your survivability mods. These along with Arcane [Guardian] give a combined EH (effective health) of over 8,000. Magus Repair might still be useful if you take burst damage. The added bonus of [Carnis Carapace]'s heavy attacks is a personal preference based on my favorite [Reaper Prime] build (see Other Considerations below). Another good Vazarin mod is Rolling Guard, but it's more expensive. If you swap Overextended with Stretch you'll be able to afford it.
• Handspring: It's very common to get knockdown-teleported, or just knocked down. This will get you back on your feet much faster for more killing and thus faster Endo.
• Despoil: Highly recommended to prevent the need to manage Energy. This also lets you switch your Focus to Madurai for 25% more physical damage with Phoenix [Talons].

Desecrate, Slash, Cold, and You

When you have a weapon with 51% or more of its total damage as Slash, killed enemies will break up into pieces. Each piece can be Desecrated individually for more chances at loot. Slash procs also apply a Bleed effect that hurts shields and bypasses armor, but enemies dying from this will not be broken apart. However, continued strikes on dead bodies will break them apart.

Cold damage is similar, although it doesn't have the constant Bleed affect that Slash has, which means less DPS but no deaths to Bleed damage.

Overall, this means pure Slash builds are best for the additional DPS, and if an enemy dies from a Bleed proc, their body is about to get slashed up anyway from several players flailing their weapons around the area.

More on Slash Damage here

Other Considerations

• Replacing the default Madurai polarity that comes with a fresh Nekros Prime with a Naramon polarity may make this build less viable for strength/tanking builds if you're using multiple configs. But if you don't forma it, you're left with a Madurai polarity mod slot that there aren't any good mods for. Maybe Cunning Drift or Rending Turn, both pretty useless.
• Magus Repair can quickly get you (and the rest of your team) back to full health if needed
• Using a Helminth for Petrify/Ore Gaze is useless in Vodyanoi - the Executioners are immune to it
• Executioners are highly vulnerable to melee damage and very resilient to ranged damage, so a melee weapon is recommended. This Reaper Prime build is my favorite so far (100% heavy attacks), but swap [Fury] with Gladiator Might because you'll be getting plenty of speed with Berserker and Wisp's Speed Mote
• I've tried loving the Kohm. I really have. But its horrible ammo efficiency forcing users to seek out ammo in the middle of the round is just not realistic, especially when Executioners are resistant to ranged damage. Get a good Slash melee weapon instead, like the Reaper Prime, Kronen Prime, Orthos Prime, etc
• On the note of melee weapons, Ripkas with the Amalgam Ripkas True Steel mod has a 100% Gore Chance that guarantees an enemy's body is broken into pieces, even if the [Ripkas] is not equipped! That being said, I don't recommend using it. Compared to other Slash weapons, the [Ripkas] hits like a foam pool noodle. It's damage is just not in the same league as many other alternatives. I believe that killing as fast as possible in order to begin new rounds faster is an overall better Endo/hour rate of farming, rather than nitpicking the act of body part desecration with such a mediocre weapon.