Shared Polarities with my Pillaging Shooter [Mesa Prime] build.

Why [Combat Discipline]? Procing Arcane Avenger for more Critical Chance and Energy Regeneration with [Hunter Adrenaline] while regenerating your own HP with Gloom as it's subsumed ability. It's quite the interesting gameplay loop of resources, which is why I do not run Arcane Energize in the build. Though you may need Zanurik's Energy Pulse and/or Energy Pads to start off the mission with some decent Energy.

If you don't have the Umbral Forma to burn, or the Umbral Mods, feel free to drop them for their regular versions and save some Forma in doing so for a similar, albeit weaker, version of this exact build.

FAQ
Why Mesa's Waltz in the Exilus slot?
Mesa's Waltz does a lot more than just letting you move/roll around while using her [Regulators]. It also ignores the wind up animation of her [Regulators] letting you begin turning the map into an Old West Tavern faster, while also allowing your focus ring reticle will grow back gradually when not firing.

What about her pew pews?
The [Regulators] build I use for [Mesa] is a standard Viral/Slash/Heat build.