Looking for best method for Cauldron Creep arm joints.

I use loose zip ties. Light gauge hanging wire would also work... You want something loose enough to allow for slop but stiff enough to actually provide a pivot point.

I've just been using zip ties for most of my movable joints.

I used zip ties at the shoulder, elbow and wrist of the "stirring" arm and fused the entire "holding" arm with screws and glue. The hands are loosely attached to the stick with a screw through the back of the hand. You will likely have to tinker with the positioning of your arms and cauldron to get the movememt smooth with no jerkyness or binding. I did my entire build with no visible support (no pvc frame) by slipping thick allthread into the leg bones a piece of steel emt counduit up the spine and using a pvc Tee hidden in the hips to support everything.