[Pilfering Swarm] is a great loot buff if used correctly. This is the higher strength variant that uses a subsumed buff ability to allow the tentacles to kill enemies.

Roar is chosen because it's one of the few abilities that increases the damage of Tentacle Swarm. Other buffs can also be run but the build then becomes a buff support rather than a low-level [Looter]. We replace Tempest Barrage because it's the weakest ability in this setup but you can also replace Tidal Surge.

Nourish, Smite, and Shock all increase the elemental damage of your weapons and even some of your abilities. This lets you save a mod slot or two on your other builds in your loadout. Nourish is the easiest to slot in as it doesn't require an augment but the other two can be run if you replace [Pilfering Swarm].

This build can also work with other damage buffing abilities like Xata's Whisper or Eclipse. It even works with hybrid defensive/offensive options like Elemental Ward or Warcry. We don't really need those buffs to kill enemies but they can help you and your team to run unconventional or off-meta weapons.

[Rolling Guard] protects you in between Undertow casts. You can eventually run out of energy so the invincibility gives you time to grab energy orbs to proc Energize. It can be replaced with [Narrow Minded] if you drop [Pilfering Swarm].

[Enemy Radar] mods help us to find enemies. Due to the nature of the build we need to sometimes seek out stragglers.

Arcane Aegis gives you additional time to roam outside of Undertow if it procs between casts. If you don't like the RNG aspect of it you can replace it with any other arcane to suit your playstyle.