(Even with the [Ignis], aim to the head. It multiply by 4 the critical damages, and by 2 the not critical.)
This build is optimise to play against ennemis out of the steel path up to the level 300.
If you want to push the ignis further, you can try this build, that have more potential damage, but more ramp-up and less QOL :
https://overframe.gg/build/569502/ignis-wraith/viral-hunter-ignis-wraith/ (the 2 need the same format polarity, you can have both and swap when you want)
But in such situation, the best is probably to take an other weapon.
Viral is a very good element, that is only weak against small Infested, but with 1 status proc, it double the damage, so even for them, it is good. With the high fire rate and status chances, it [Reach] 10 procs in around 1.4 secondes, if the ennemis are not dead before.
The fire status is a very good control, and reduce armor.
If you use corrosive damage, you will have more damage on ennemis with Ferrite armor (most of the greener), and less on the others ennemis.
About the arcane : the 3 have their ideal contexte of use. Deadhead start to be interesting at high level (~ lv100+) when you start to care about headshot. Merciless give lot of damage without need to car about anything other than kill ennemis. And the one for melee is interesting if you also play melee.
The [Ignis] deal damage in a 3m radius around where it hits, and [Primed Firestorm] increase it to 4.3m radius. it is not needed, but help to clear fast multiples ennemies.
(The exilus mod is not important, use what you prefer. The main possibility are : [Sinister Reach], [Vigilante Supplies], [Agile Aim], [Aerial Ace], [Twitch].
you can also not use any, and save a format and an exilus adapter.)