Howdy folks!

For me, the companion should provide [Enemy Radar] and collect the resources while providing utility during combat. Also it's important to be hard to kill so you won't lose your little helper during the mission. Panzer Vulpaphyla does that (well it's basically immortal) and spreads viral procs everywhere around.

Mutagen and Antigen:
I went for cosmetics (although the mutagen determines the health type of the vulpaphyla and the antigen gives you a polarity type).

• Zarim Mutagen - tantacles tail - I went for the Nine-Tailed Fox look
• Plagen Antigen - scales around the neck + a Naramon polarity

Let's talk about the mods:

• Primed Animal Instinct + Fetch -> Those 2 give you the ability to see the enemies on the map and grab the loot when in close proximity.

• Primed Pack Leader -> Press E once or twice and your companion will be back to full hp.

• Link Health + Link Armor -> Vulpaphylas are immortal but the larva form loses some of it's perks so we should try to avoid it.

• Hastened Deflection -> Since shield gating it's a thing, it's better to have a small shield which regenerates faster instead of a big slow one.

• Viral Quills -> Special mod available only for Panzer. It turns her into a Mini-[Saryn] which will spread spores. 40% status chance for viral procs it's good enough damage wise so I decided it doesn't need any other damage mods and it can focus more on survivability and utility.

• Synth Deconstruct -> Panzer Vulpaphyla can damage all the enemies if you spread the spores.

• Panzer Devolution -> Each Vulpaphyla type has it's own devolution mod (it does the same thing, only the name and the extra effect are different). This makes your pet immortal. When it dies, it devolves into a larva form (floats above the warframe like a robotic sentinel) and it still has Animal Instinct active. After 30 seconds it will turn back to it's usual form.

• Martyr Symbiosis -> Since those pets are immortal, you can '[Sacrifice]' them to keep you alive in tight situations.

***A few words about Shield Gating

Shield Gating is an effect that occurs when shields are fully depleted, which prevents any excess damage leaking into the health pool. Warframes, Companions, and Necramechs gain 1.3 seconds of invulnerability upon hitting the shield gate, only resetting when shields are allowed to fully replenish. If the shield is still in the process of recharging after the gate has activated, the shield gate will only last for 0.33 seconds.

Other viable mods choices:

• Animal Instinct - It can replace Primed Animal Instinct if you don't have it.
• Pack Leader - It can replace Primed Pack Leader if you don't have it. Actually you don't even need the primed version, I used it just because I have it.
• Hunter Recovery - Since Panzers spread spores, they do a lot of damage which can be converted into heal for your warframe.
• Synth Fiber - Extra armor for your companion is always welcome. Also it has good synergy with Synth Deconstruct.
• Tek Assault - Your pet can cheat death with it but is not a big deal because in 30 seconds it will revive itself.

*PROS and CONS*

• It's immortal
• Deals viral procs with only 1 mod
• Can save you in tight situations

• Smeeta Kavat provides more utility

Conclusion

Panzer Vulpapyla it's arguably the best option if you want an immortal companion. It doesn't provide the same utility as Smeeta Kavats but it can save you if needed.

Check out my other companion builds:

• Carrier - Your ammo buddy
• Djinn - Self revive companion
• Adarza Kavat - Critical Eidolon Hunter
• Smeeta Kavat - The most useful companion