This is my personal Ultimate OVERKILL Umbral Helmsman. Jack of all trades, usable in any content.

Helminth
I choose to subsume nothing on [Sevagoth]. His 1 and 2 are mandatory, and 3 is very good. What about his 4? Many builds subsume Roar or Nourish over his Exalted Shadow. The reason why I don't is that his 4 represents his entire identity as a Warframe. While his shadow isn't as amazing damage wise as simply pressing 2 and 1, I can't bring myself to remove the Warframe's identity for a Helminth which offers extra damage. Moreover, his shadow offers gameplay variety while you're in a mission. If you ever get bored of shooting things or pressing 2 then 1, then you can use your shadow for some difference in gameplay.

If you really [Hate] his shadow with a burning passion, feel free to subsume roar on this build, but for my money and time, I'd just pick a different frame.

Archon Shards
1-2x Tauforged Casting Speed
3-4x Tauforged Power Strength

Arcanes
These arcanes work best for me. Molt augmented allows this [Sevagoth] build to hit Gloom cap with 3x Tauforged Reds. Arcane Energize helps with energy economy. I also bring an Energy Generator(/items/arsenal/2236/dethcube/) with me most of the time.

Have fun!