[Pilfering Swarm] is a great loot buff if used correctly. This is the higher range variant that uses a subsumed CC ability to counteract the random tentacle spawn area.

Ensnare is chosen because it pulls all enemies in the area into a neat ball so that Tentacle Storm becomes more consistent. Undertow already allows you to do this but it requires you to individually click on each enemy. Larva also works but to a lesser extent due to needing either another augment or lower duration respectively.

Quiver and Resonator are also good support options for this build if you have a way to deal with the random tentacle spawns.

Tempest Barrage is replaced, but if you want to run the Corroding Barrage augment then Tidal Surge is the next best choice.

Additional Augments are run on some variants to this build. [Augur Reach] or [Streamline] are the weakest mods depending on which augment you're looking to run. Remember to switch mods around to fit into the polarity plan.

[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.