Anyone who says Onos is a bad incarnon is self-reporting a massive skill issue. [Onos] is amazing, you just have to know how to build and when to fully charge it's incarnon shot or not. With this build, majority of fodder enemies die without even charging the full shot, meaning the incarnon will last a lot longer. Leave final shot to big groups and eximus/stonger enemies. If there are any other mod suggestions let me know and I will test them and edit this accordingly.

INCARNON UPGRADES:

I: Incarnon form

II: +25% fire rate

III: +30% reload speed

IV: Headshot gives +50% incarnon charge (do NOT use Elemental Excess, 10% base crit is a LOT of damage missing and is why a lot of people think [Onos] is bad.)

V: Crit Chance and Crit Damage increase by +5% when your beam hit an enemy. Stacks up to 50 times.

MOD BREAKDOWN:

Galvanized Diffusion: Mandatory multishot mod

Primed Pistol Gambit/Primed Target Tracker: Mandatory CC/CD

Lethal Torrent: Extra Multishot and a nice Fire Rate increase to help the incarnon form out.

Pistol Pesilence/[Frostbite] to make Viral. (Mod placement matters, you might make a different element if you place it differently.)

[Scorch]: This is what you would replace with a riven mod, but with this, it's a really easy Cascadia flare user and buffs your final shot a lot. If you replace this mod use secondary Merciless.
Yes, even with [Hornet Strike].

[Ruinous Extension]: This is not mandatory and is mostly up to you. However, it is a really nice quality of life.

[Hornet Strike]: I use this over [Galvanized Shot]. This is somewhat personal preference between the two, but in my opinion, a lot of damage comes from the prefire, and [Hornet Strike] buffs both of them compared to [Galvanized Shot] only buffing the end result.

OTHER MOD OPTIONS:
These would all replace [Scorch], which would make you switch Cascadia Flare as well,

[Magnetic Might]: A strong eximus killer with even more Crit damage. Really underrated mod, its not even listed as an option to put in Overframe yet. It might honestly be better to slot this in over [Scorch] completely, but they produce similar damage in my testing and Secondary Merciless is harder to keep up than Cascadia Flare for [Onos].

Primed Heat Charge: I don't have this mod yet personally, but using this over [Scorch] might add a good amount of dps, but lower the status chance. Up to you.

[Accelerated Isotope]: It's a good mod in general and the fire rate is nice, however, you already have enough radiation in your weapon—just a good quality of life.

Pistol Elementalist: It's a fine mod, however, this build one-shots and doesn't rely on heat procs to kill the enemies.

If there are any questions or suggestions comment and I will reply and test to the best of my ability!