Basically, this build works very well in Steel Path, but you'll need to use either Xata's Whisper, Eclipse, or Roar for instant kills beyond level 200. Proboscis Cernos is a Steel Path single-shot crowd-clearing beast, but it doesn't work well against SP bosses like Acolytes. Therefore you should bring a boss-slaying weapon such as a [Kuva Nukor] or [Pyrana Prime]. Also, you can use the regular mods if you are missing the Primed, Galvanized, or Amalgam mods. If you don't want to use Primed Faction Smites then just use [Heavy Caliber] instead, it will fit. [Amalgam Serration] fits too if you enjoy the sprint speed QOL. If you are using some kind of damage buff then you can exchange [Serration] with Primed Firestorm for some additional Blast Radius QOL.

Enjoy :)

Unnecessary Essay below

Mod Breakdown & Alternatives:

• [Arrow Mutation] is there because it has a low magazine and I will run out of ammo otherwise. This is not a critical chance weapon so vigilante supply is not worth losing precious ammo for the 5% critical enchantment. If you want to turn [Proboscis Cernos] into a Status Critical Hybrid, then I would instead suggest equipping a Vigilante buff sentinel weapon for the +20% Critical Enchantment (See more details at the bottom of this guide).

• I use a [Galvanized Chamber] for the multishot, more multishot equals more arrows which means more explosions. If you are missing it then use Split Chamber and Vigilante Armaments.

• [Serration] is there for the base damage, if you use Smite mods too then you will gain more damage since it double dips on DOTs like Gas and Electric. You should switch them as appropriate to instantly kill enemies in Steel Path, the only ones that matter are grinner and corrupted banes since they are the toughest factions. This build is very good against the Corpus and Infected, so you won't need a bane mod against them. If you don't like to switch them as appropriate then just use a Heavy Caliber, as it works too but this won't double damage dip.

• I use three 60/60 mods to bring the status chance over 100% status chance since that is the sweet spot where [Proboscis Cernos] works best. I specifically use Gas and Electric for AEO damage because the tentacles bring enemies into a tight cluster. Therefore enemies will take multiple instances of Gas and Electric procs. These are instantaneous damage procs that damage everyone around them in an AEO, unlike Heat and Toxin procs which are single targets and have a cooldown of 1 second before functioning. Also, Gas lingers behind so it can hit multiple enemies in chokepoints, and Electric stun so it has a very nice crowd control too.

• Primary Merciless is the best because [Proboscis Cernos] is an explosive weapon that will kill multiple enemies quickly and the reload bonus is very nice too. Primary Dexterity can work well too if you are a melee-centric warframe player. I would avoid Primary Deadhead even if it provides bonus headshoot damage to explosions because aiming headshoots is very difficult with its nasty arrow curve unless you are making up for it by using [Terminal Velocity] as well. However, doing that will mess up your ammo economy, so don't use Pimary Deadhead because overall it's not worth it.

Note: If you are playing casual Steel Path, then you can just use both [Serration] and [Heavy Caliber] because you do not seriously need Faction Smite mods before level 400. For Endurance runs, this build is best paired with [Xata]'s Whisper for quadruple dip DOT damage through Primed Smite mods. I would typically use a [Saryn] with a [Venom Dose] for Corrosive and Xata's Whisper but any warframe with Xata's Whisper will work very well too. If you don't have Prime Sure-Footed, then warframes that provide over guards like Frost or Rhino can become immune to radial explosion self-stagger effects. If you are too lazy to change Faction smite mods between missions, then any warframe with Roar will work great for you as Roar provides inbuilt faction damage. Also, Eclipse can become stronger than Roar if you know how to use it well. I would avoid using Galvanized Savvy because the bonus damage doesn't affect AEO explosions.

Short Vigilante Buff Guide:

• If you have a sentinel gun such as [Sweeper Prime], then you can take advantage of it by equipping all 4 Vigilante mods in its mini shotgun to obtain the Vigilante mod set bonus. It will give you jailbroken 20% critical enchantment, which pairs well with any primary. Jailbroken, as in that you don't need to equip any Vigilante mods into your primary to retain the bonus, and equipping more vigilante mods into your primary won't increase the effect. However, you can equip Vigilante mods into your warframe if you want, Vigilante Pursuit is quite good.

Carrier Prime build: https://overframe.gg/build/468562/ Replace it with Panzer or Djin for SP Endurance.
Sweeper Prime build: https://overframe.gg/build/485975/

Instead of the general audience, this build was initially created for my [Saryn] with [Xata]'s whisper to instantly nuke everything to death. Alternatively, any warframe with [Xata]'s whisper, Eclipse, or Roar will work very well too. Regardless, this Probosis [Cernos] build is strong enough to kill everything on casual Steel Path without those damage buffs being needed. Thanks for reading so far, I hope you enjoy it :D