I just spent about 5 minutes trying to find a pic on bricklink but I can't find them, not sure what they're called but they're those 2x2 bricks with technic axle hole through the middle, one with the ball joint and one with the socket joint.
So far this has been the most difficult MOC I've worked on, all the curves are difficult to achieve on all 4 sides and still make stable. Once I've nailed down the torso shape I'll likely have to pull it apart and rebuild it so it's stronger. I've already done the head from ages back (probably over a year ago)
The mouth is just photoshopped on for now to test...
I think I'll try and change the hat a bit too and try and get rid of that gap somehow between the head and hat. The most difficult part I reckon will be the arms, maintaining the curves on a smaller scale is gonna be tricky.