Also, what types of weapon mods can Ignis use? The wiki mentions adding more elements to it, and it mentions Wildfire, but can it use other rifle mods then? What ammo does it pick up? Ditto for the rocket and grenade launcher. It seems like a good weapon for Vauban.
The Ignis uses standard rifle mods and ammo. Weapons that deal innate elemental damage can be combined with other elemental mods to change the overall output of the weapon. For example, adding Cryo Rounds to the Ignis would change its output to be 100% Blast damage. I have 3 elements on each of my 3 Ignis loadouts; the first two combine together to take care of the faction weakness and the third one combines with the innate Heat damage of the weapon. The Arsenal numbers on my Grineer loadout are something like 1200 Corrosive and 1300 Blast.
Oh, and the Ignis is a great weapon for
any Warframe against Infested and (to a lesser extent) Grineer. There's not really such a thing as "good weapon for X Warframe." There's good weapons for squaring off against certain
factions, but that's mainly it. After the next patch it will get even more complicated since the individual units
within a given faction will have different weaknesses as well.
One could say that Damage 2.0 is obnoxiously convoluted, but it is what it is.
