Obviously can be optimized a bit more but it's just a proof of concept for now.

LOADOUT:
Felwinter's Helm: Linear Targeting, Sniper Targetting
Arms: Linear Dexterity, Linear Reloader, Charged Up
Chest: Unflinching Linear, Void Damage Resist, Reaping Wellmaker
Legs: Sniper Holster, Elemental Charge
Bond: Bomber, High Energy Fire
Witherhoard
1000 Yard Stare with Quickdraw, Snapshot
Cataclysmic with Fluted Barrel, Enhanced Battery, Reload Masterwork, Enhanced Fourth Times the Charm, Enhanced Bait and Switch
Vortex bomb with Child of the Old Gods and Feed the Void, with Echo of Remnants, Expulsion Dilation, Undermining

Clarification on video title - I labeled it as a proof of concept as this was attempted with very little optimization in terms of stats/mods. It was just meant to demonstrate that the concept of Kell Echo solo 1 phase is possible, and that one may build upon what was used in this demonstration in a full run.