Honestly really wanted to keep this a 0-Forma build, additionally I wanted to keep any primed mods off it because these can be prohibitively expensive and/or difficult to get. I achieved this, sorta. You can achieve 0-Forma by keeping the charged shell at level 0. This brings average hit to 19,260. I think 5k damage is worth it, but I don't think the 1.6k-ish damage from going to the current top-ranked index plasmor is.

If you want to increase this build to a 2, or even 3 forma, consider these (sorted by damage):

• Primed Point Blank +5390.5 damage/avg hit
• Primed Charged Shell +4953.4 damage/avg hit
• Primed Cleanse Corpus +4699.4 damage/avg hit

Pick any two for a 2 forma build, all 3 requires 3 forma.

You do you, 1 forma for 10343.9 damage/avg hit is pretty good, use them if you have them and if you have the forma. This still performs to medium investment round 5+, probably works for prodman runs but I haven't tested that yet.

If you wanted to you could drop in some magnetic damage as well by swapping in [Frigid Blast], or [Chilling Grasp]. (magnetic needs to be put first or the heat mods will combine with cold to produce blast, or the electric mod(s) won't combine with the cold by preferring the innate radiation, this does yield a pretty swanky rad/cold plasmor though).

you get 300-ish points worse damage swapping vigil armaments for cleanse corpus, at least according to overframe's algorithms. This may be worth it for a more general-purpose build so consider it if that's your intent.

Additionally for a general-purpose build you may want to consider shotgun spazz (or the amalgam variant), or any of the many reload speed mods. These are largely irrelevant to the index since there are only at most four enemies at any given point.

Feel free to swap in some toxin if you prefer, though I have good results with pure radiation as my chosen compromise element for index, if there was a way to guarantee only the humanoid enemies you probably would benefit more from toxin, but with so many robots radiation just works better ( at least if you don't overstrip their armour, if you do you'll have to find a build targeting their health types, flesh and robotic. The only thing neutral to both is corrosive*, you could tradeoff -25% for slash or toxin in that case but it's just not ideal)

*honestly if you're overstripping there's a nonzero chance that's your element of choice to begin with.