First thing first, this build is created by my clanmate ArcticTFoxy and modified a bit by me. I choose more Range over Duration, that's main difference between ours builds.
The playstyle is kinda intensive so I hope you are ready. As far as [Lavos] is already tanky, we need to make him an ubertank, right? So here's Umbral Forma and all Umbral mods. But we need more! [Adaptation]! MORE! OK OK... Arcane Grace and Arcane [Guardian]! Now we're talking! Ubertank! And when shit hit the fan, we got [Lavos] first skill, Toxin Ophidian [Bite]! This one will heal us for almost 31%! That's nice!
OK, now all the [Juice]! Gameplay!
Hold to imbue! Make Corrosive + Vial [Rush] and Viral + Transmutation Probe (or opposite) and probably would be the best if you make Gas + Catalyze just to make your life easier! Any enemy will melt, doesn't matter level, Status proc. will do the trick, and of course help yourself with guns and melees for MVP.
Here's the tip of how to build Combined Elements:
I suggest you use companion with Synth Fiber on it... like this Moa - My name is Legion, for we are many.
Try not to break your keyboard ... or your fingers :)