The motto of this build is a high investment of forma equals high returns of damage. I use a Warframe with Nourish for Viral Damage that's why I didn't include Viral in this build. This build is for Nourishbros, with Slash and Heat to infinitely scale from the Viral. Heat stuns so it opens up easier headshoots. I use both [Steady Hands] to reduce recoil and Secondary Merciless to increase reload speed. This build is going for raw critical elemental damage because it will cause the double Pyrnaa effect to be activated very quickly. This setup alone easily shreds everything on Steel Path.

Note: For Casual Steel Path just use [Hornet Strike] or [Carnis Stinger] instead of the [Primed Expel Grineer]. For Endurance runs, replace Faction smite mods as appropriate because they will double dip on Heat and Slash for even more DOT damage. This is already a million of DPS before even considering the DOT damage and Nourish Viral damage bonus.

Even if this build wasn't intended for general use, it remains very powerful even if you don't have Nourish. Enjoy :)

Disclaimer: If you don't have Nourish then replace [Galvanized Shot] and [Primed Expel Grineer] with both [Pistol Pestilence] and [Frostbite]. It will give you the right amount of Viral with the correct status weight compared to Slash and Heat. It will fit with this Forma configuration but it has less damage according to Overframe, don't listen to it because it doesn't calculate Viral's status of up to 325% bonus damage.

You can ignore the essay below.

Note: There is this misconception that Pyrna is a status pistol and should be built like one because it lands statuses. That is somewhat wrong and the statuses are better attributed to its high Multishot resulting in a high pellet count. On my test in the Simulicrium, Galvanized Diffusion has helped me land more statuses than equipping multiple 60/60 mods and [Sure Shot]. For me, simply using Galvanized Shot to turn this Pyrana into a hybrid status pistol has worked better than investing in more 60/60 mods as if it were a status pistol for real. The only 60/60 mod I would consider using is [Carnis Stinger] if you don't like Expel Faction mods. Also, you could change Primed Heated Charge and Main for Corrosive mods and combine it with 2 emerald archon shards that increase corrosive max stacks for a single-target full armor strip.

Optional: Expel Faction mods can be exchanged with [Galvanized Crosshairs] if you are aiming for heads. Aiming for heads will deal more damage especially if paired with Secondary Deadhead. I also had a lot of fun using the [Combo Fury] mod with Secondary Dexterity as it turns [Pyrana Prime] into Shark Prime. I simply throw my melee and receive bonus reload speed and increased magazine size on my [Pyrana Prime] and it goes dual mode even more easily, in fact too easily as it drains all my ammo. Nowadays, I use Cascadia Flare instead of Secondary Merciless, but I didn't include it in the build since I know not everyone has it, but Cascadia Flare provides more DPS than any other Secondary Arcane I have mentioned so far. If you really desire to further Min-Max [Pyrana Prime] then you can equip an Arcane Velocity on your warframe for even higher DPS but there will be a higher ammo price. Another option is using Arcane Avenger because Orange Criticals would become common, It's a bit less DPS but it consumes less ammo. Arcane Pistoleer solves ammo problems if you find yourself lacking them. For melee equipment, you can equip any [Furax] with [Amalgam Furax Body Count] to obtain a nice +45% Fire Rate for Secondary weapons. For Archon shards, Crimson and Topaz are great if you want to invest all into this build here.

Optional Combo Fury Glaive build: https://overframe.gg/build/526760/
and
Optional Ammo Carrier build: https://overframe.gg/build/468562/

Thanks for reading so far, have a nice day!