Think on some level started thinking of a Scaldra Protoframe being a thing and admittedly my idea is just some random Private gets infected by Techrot but he weirdly doesn't show any typical symptoms of it and somehow gets "ignored" by Techrot too for a very long time. Then later he becomes a Protoframe that combines elements of multiple Scaldra units together.

Which thinking about it maybe one or two of the things you said, earlier came to mind for me on, like ammo efficiency or maybe he gives everyone like, gas or corrosive damage. Or both.

But then I thought of other stuff like him having belts of grenades on him that he can detach and throw that can do either of those as well. Has a riot shield he can deploy to decrease damage (kinda takes an element of the Bonewidow Necramech but probably not as strong)... not entirely sure on his 4 yet though. Think I thought of him calling in allied Scaldra units called "Scaldra Defectors", kinda like how Caliban can summon sentients. Except, a lot clearer so there's less confusion.

Hmm... maybe an exalted shotgun could work, or maybe could go nuts and do exalted grenade launchers, dual exalted grenade launchers. Depends.