The miniature that has caused the most problems for assembly so far is the Grendlr - with the two parts of the body being warped so they do not fit correctly. I shot a video for how to handle that issue, and we found it worked very effectively. There is a similar issue with the Cthonian - but it's just one of the legs that has warped, causing problems with the way it fits on the base. Again, this was pretty simple to fix - I just dipped it in very hot water (being careful), and re-shaped it slightly.
I found the best way to do this was to attach the left leg first (as that fit correctly), and then correct the position of the right leg, lining it up by standing the miniature on it's feet while the leg cools.
The other thing I did on this one, was to pin the arms into place - this is not strictly necessary, but where there is a large part attaching to a small area, the increased leverage make it quite likely to break off if dropped. I just drilled a hole in the end of the rounded part of the joint - glued a short length of brass wire in place (a little bit of paper clip would do just as well), and then drill a corresponding hole in the gun. The two parts are then glued together. There is one part that is optional - the face plate. If you want to add that, it just attaches to the front of the head.
Here are the parts for the Cthonian -
Here is the fit between the right leg and the ground before it is fixed, the left leg is glued in place here -
Here is the fit after the right leg has been dipped in hot water and held against the ground while it dries, and is then glued to the base -
To pin the arms in place, I drilled a hole in the body half, then inserted a short brass pin -
Then the arm was glued in place, and I did the same for the opposite side -
Here is how the optional face-plate fits -