Kind of an odd build, but an effective one.

The Mecha set synergizes very well with [Lavos]' kit. Any time a marked enemy dies to one of the many status effects you'll be throwing around, all of those status effects and all of that damage spreads to enemies in range. This will often lead to you rapidly stacking statuses on enemies since [Lavos]' abilities have pretty good areas of effect.

Efficiency can be left neutral, since Transmutation Sphere reduces your cooldowns based on the number of enemies that get shocked. [Umbral Vitality] and [Adaptation] give you a lot of survivability. [Stretch] gives you plenty of range, and [Umbral Intensify], [Transient Fortitude], [Power Drift], and Augur Secrets give you a respectable amount of strength.

The arcanes have been left open since Lavos is fairly arcane-neutral. Guardian is a good choice, but it tends to be a good choice on a lot of frames. You could just as easily go for weapon-enhancing arcanes like Strike or Precision, Tanker to take advantage of Transmutation Probe giving you tons of universal ammo, or even a Theorem/Residual combo if it fits the rest of your loadout.

Two notes:

1. You can dunk duration if you want, since by the numbers it only affects the duration on Vial [Rush]. However, [Lavos]' hidden passive means you want at least neutral duration. You get bonus status duration for both your abilities and weapons that scales off duration, which gives more time for all those status effects to do some work.
2. The Mecha set is worded a little vaguely. The key to success is that for status effects to spread and kill other enemies, the marked enemy has to die directly from a status effect.