For use with my Titania Build

Update 38.5 changes, round 2:
Augur Pact -> Primed Heated Charge (1 forma)
Pistol Pestilence -> Frostbite
Primed Expel X -> [Pistol Elementalist] (1 forma)

This build synergizes well with my [Titania], allowing it to abuse [Xata]'s Whisper's interactions with Blast and Secondary Enervate to spam AOE red crits and proc armour stripping with Archon Continuity. Fire rate mods aren't used because they only stack additively with the bonus from Razorwing Blitz - over +300% in my case.

Flex Spots:
The best place to add a faction mod is over [Merciless Gunfight] or [Pathogen Rounds] (if armour strip is not necessary.) I don't use faction mods much anymore since 1999 enemies don't have any and switching them around is annoying. It is worth considering however that faction multipliers have very wonky math with [Xata]'s Whisper as well, allowing the bonus to double or triple dip in ways I don't entirely understand, but the results don't need a math expert to explain them to you. That said, this is unnecessary except against enemies with damage attenuation or at level cap. [Titania]'s damage is so absurdly high I find it hard to tell sometimes which options are actually higher DPS. You'll probably only 'need' a faction mod for level cap or bosses with attenuation, like The Fragmented.

Punch through is less useful depending on the angle you're firing from, but when it works, it effectively doubles your damage. [Titania] can spend a lot of time in the air above enemies, but I like to use it because her damage output is so high anyway, it ends up being more useful than more damage that would do nothing except overkill. Secondary Enervate makes the extra crit damage contribute a lot, though.

Other good DPS mods to consider based on your needs are Magnetic Might and [Hornet Strike], which can replace Pistol Elementalist against enemies that are affected very little by status, Merciless Gunfight if you're not big on punch-through, or [Pathogen Rounds] if you don't feel like the armour strip is necessary. I would not recommend removing any of the other mods in any situation except extreme niches like enemies who are status immune entirely.

Potential comfort options are (Primed) [Steady Hands] to avoid nausea from high fire rates (you can also choose to only fire when zoomed in, as this negates all recoil on this weapon) and [Tainted Clip] (reload modifiers do nothing, negative or positive) if you want your [Flow] interrupted just a little bit less.

Blast?
While Blast isn't actually that good on single target weapons, it becomes a bit ridiculous with the combination of Blast and [Xata]'s Whisper due to some wonky Warframe Math™ that I honestly don't entirely understand, but the results speak for themselves. If you're not running either of these things, it will do practically no meaningful damage.

Toxin?
Toxin with [Archon Continuity] is a DOT, armour strip, and generally strong damage type with no resistances. The damage of the DOT is increased by power strength, the razorflies damage multiplier, faction mods, toxin mods, Magnetic and Viral, and base damage mods like [Galvanized Shot], [Hornet Strike] and [Augur Pact]. Each of these increases are multiplicative with each other. Dex Pixia procs hundreds of statuses per second and this allows you to spray and pray all over a room - enemies that live the initial hit will die to toxin soon after, effectively reducing the time you need to shoot at each enemy by a significant amount with decent luck and a bit of practice to get a feel for when enemies have enough procs to finish them off. The armour strip it provides also makes blast procs deal even more damage.

[Suppress]?
None of the exilus mods are that great on [Dex Pixia]. The recoil is perfectly manageable (though you should use Primed [Steady Hands] instead if you get motion sickness or get annoyed from it, that's what I do.), it already has pinpoint accuracy, ammo maximum and ammo conversion have no effect, you can't slide or aim glide, extra move speed while aiming can only be a detriment, and while projectile speed does influence damage falloff a tiny bit, I don't find it to be significant - you're still playing the fastest frame in the game, after all, and she's not lacking in DPS. That leaves [Suppress]. Enemies already usually choose to shoot at anything else before [Titania], particularly razorflies with their aggro capabilities, and [Suppress] just makes it a little bit more consistent. Enemies are drawn to sounds even if you're not hidden, and will often target the loudest enemy. With a silent weapon, they will only take extra notice of you shooting if you're within a very short distance, which you're almost certainly not while playing [Titania]. TLDR, it's a small survivability boon. But if you don't want to spend more forma than necessary, you don't need it.

The case for [Hornet Strike]:
This is taboo for some reason, but you may still actually want [Hornet Strike] somewhere on the build. If not just for comfort, it still works better than some would lead you to believe for large crowds, needing less ramp up for every individual enemy, and being much stronger for bosses where there are no weaker mobs to kill to proc the stacks. (archon [Hunt], phase one of the fragmented, some steel path assassinations) This means on average your time to kill can actually be lower in many situations with [Hornet Strike] vs competing mods (which are only marginally higher under 100% optimal conditions anyway) unless external factors apply status priming to all enemies before your first bullet lands. (squadmates, razorflies, and punch through help a lot with this, to be fair!) Flip the "Apply Conditionals" button for a demonstration next time you're in the build editor. Ultimately, if you don't like it that's your choice, but you should make that decision for yourself based on practical feedback and experience rather than what produces the highest number in a simulator. Enemies only get so tanky.

Keep in mind that Overframe cannot take Nourish, [Razorwing Blitz], Arcanes and so on into account, but I do. Don't blindly trust the percentages it tells you are higher in a [Vacuum]. Mods Overframe suggest are better like [Lethal Torrent], [Accelerated Isotope] and [Primed Heated Charge] perform worse than the recommended mods because the fire rate bonus amount has no practical impact when Razorwing Blitz already grants 300% or more fire rate, and the multishot/radiation bonus being more or less alone is weaker than these options, or because they replace a more useful status with a less useful one.

If you think I've actually made a mistake, and you can get better results with a different mod setup, show me evidence comparing the two and I will replace it and credit you. If you can't do that and just want to tell me that I'm smelly and my build sucks without showing your work or making a case for yourself I'm probably just gonna laugh at you instead.

Other statuses:
A case can be made for dropping Toxin entirely and adding even more blast weighting - generally though you don't need the little bit of extra blast, and you'll miss the armour strip in cases where it is useful. Try switching [Pathogen Rounds] for [Pistol Pestilence] and see how that performs before dropping it completely.
Heat is effectively just a worse Toxin when you have [Archon Continuity], and is incompatible with Blast.
Viral and Blast are incompatible, and blast becomes a lot weaker without [Xata]'s Whisper if you were to gain it by running Nourish instead. I suggest going full toxin if you run Nourish. I think heat inherit is pretty overhyped, if you need 1000 heat procs to kill something, you're probably building wrong. This build can more or less one shot anything at any level except bosses that have status caps anyway.
Electric is pretty weak without any source of armour strip - and if you build for it, you won't have [Archon Continuity] to fill that role for you anymore. It might be better in organized squads with another player stripping armour, but probably not by much.
Corrosive is built in because we run with [Archon Continuity], and deals no damage. Thus even though it is higher damage VS Grineer, toxin ends up doing higher DPS anyway.
Gas isn't great for this kind of weapon because it has a stack limit of 10 and the [Dex Pixia] can apply hundreds of statuses with sustained fire in just a few seconds. If you like to run [Mag]'s pull or similar grouping abilities it may perform better, but I think in most cases punch through is sufficient.