I tried to search but failed to find any info so I’m asking here. Does Rampager obtains immunity to non-elemental damage after the first phase? Because from my experience he does. At least on Mayhem 3 (in both Normal and TVH modes). He still gets damaged by my Jabber’s pistol but my non-elemental weapon stops dealing any damage.
And the second question: which element is best to kill the Rampager faster. I know that it should be Incendiary but it takes for me a pretty long time to defeat him with fire-damage-over-time weapon.

His first phase he is resistant to radiation, but after he swaps to corrosive if fire isn’t working then it’s not a bad choice either.

Cryo doesn’t have a negative multiplier either

Moved to spoilers.

I hit him pretty hard with ne Jakobs weaponry on my first encounter. I think I remember seeing some “immune” text pop up from time, possibly between phases or during his summons of the minions? Based on the fact that I beat him down quite handily, I don’t think it’s permanent (or at least not meant to be permanent)

Do you mean that whilst not in specific moments (like changing a phase or summoning) he was vulnerable for Jacobs guns?
In my case I can beat first phase in literally few second with Fade Away + King’s Call, but then I starting to straggle to decrease his health just for a bit.

Thanks, will try radiation.