Now we will finish having fun with Gunnery Sergeant Chikibi. Based on Catachan Imperial Guard Gunnery Sergeant Harker, Sgt Chikibi's main weapon is also a Heavy Bolter used without the need for a loader assistant.
Strapped to the lower right arm is the 'Terrordactyl', which is huge enough to have a mind of its own. Which is good, because Chikibi has 4 arms and a prehensile tail to think about. Also not spilling his pipe.
Terrordactyl is based on the Heavy Bolter that came with the Rogue Trader Space Dwarfs weapons sprue. It has been given life with eyes created from some inset gem bits from some creature that did not deserve such finery. Terrordactyl is part Tyranid like Chikibi. In this case, the claw comes from an Epic Lictor. The large spikes at the rear also come from the Tyranid Biomorphs sprue, with small spikes snipped off of the Dark Eldar Warriors that everyone was super-happy to get in the 40K 3rd Edition set.
The "rear leg" is a sword handle from a mid-1990s Orc Regiment sprue. Of course, the ribcage and spine are from the venerable Skeletal Horse. And I still have a baggie of Skeleton Army bits for the future.
The color of the body of the weapon comes from using a very old version of Bad Moon Yellow, right out of the Ork & Eldar Paint Set, that is translucent and good for nothing other than acting as a glaze over darker shades.
The last thing seen by enemies of the Hungry Ghosts.
Assessing the possibilities...