How do I stop my knight builds from falling apart when I attach horse barding?

I run into the same barding problem on my castle builds and the answer is basially that the neck clips were never meant to hold that much side weight. What's helped me is adding a little counterweight inside the saddle instead. If you put a small 2x2 plate or a couple of tiles in the saddle hollow opposite the wing elements, the whole assembly balances and the clips stop being pried outward by gravity. Sounds silly but it works. Also check that you're using the newer horse body with the deeper clip sockets, some of the older horse molds have much shallower clips that just will not grip heavy barding no matter what you do. For the crest, friction alone is a losing battle with a great helm. The stud on top is smooth on most of them. What I do is put a small plate with a clip or a single stud between the helm and the crest piece so the crest connects to something with real grip instead of sliding on the dome. If your dragon crest is built around a bent tube, try threading it so one end hooks under the helmet rim and the other clips to a bar on the crest. A two point connection stops the swivel that makes it slide off when you pick the fig up.

On the polearms, the drooping is the hand clutch power wearing out, and heat or squeezing won't fix it for long. Cheapest fix is swapping in fresh hands from a fig you don't display, hands are a few cents. Some people file a tiny flat spot on the shaft near the grip but I've had mixed results with that. Rotating the weapon 180 degrees in the hand sometimes helps too since the droop direction flips. And honestly for a shelf diorama, a drop of clear silicone on the wrist joint is invisible and reversible with some careful peeling, it's the only thing that has held up for me long term.

Mostly lurking here since my main thing is a big pirate ship display, but the drooping weapon thing got me too. What fixed it for me was wrapping a single layer of masking tape around the shaft right where the hand grips it. Bulks it up just enugh that a worn hand clamps down again. Took two minutes and you can peel it off if you hate the look. I only display mine so I can't speak to how it holds up with play, but on a shelf it's been fine for months. Also curious about that saddle counterweight trick, does the plate sit visibly or is it hidden once the rider is on?

Seconding the counterweight trick, it saved my mounted griffin knight last month. I went one step smaller and used two of those thin 1x1 round tiles stacked in the saddle hollow and that was enough on its own. Also noticed the same thing about the horse molds, my barding only stays put on the newer body I got from the recent castle set, the one from my childhood bin pops off if I look at it wrong. Curious if anyone has found the reverse problem, where the barding sits too tight and scratches the paint off the clip.

The barding thing I solved a diffrent way on my mounted builds: I stopped making the neck clip do any work at all. Mine mounts on a 1x2 plate that also snaps onto the saddle studs, so the clip just lines the piece up while the saddle carries the load. I build display cases for a hobby shop and it's the same logic we use with figure mounts, load path matters more than grip strength. For the crest, double check your great helm because some of them have a small stud on top. Mine did, and one round plate on that stud gave my horned crest enough bite that it stopped spinning loose when I pick the fig up.