Where can I find that 2H rifles please ? I guess it is a MI, but not sure about it
Some of the Fleshwarped Trolls can carry it or the Aether version I think? They tend to show up in the fields around Homestead and the areas afterwards that contain Aetherials like the Plains of Strife.
The Fleshwarps Trolls that throw Blackwater Cocktails are the ones that drop the Fleshwarped Incinerator.
It’s a monster Infrequent from the Fleshwarped Flameeyes and, according to the Gamepedia, they can be found in Act 3 and 4 Regions