New to Lego building. Need help with making a Lego Garchomp

I'm very new to lego building and was using a base design from user: eyemcantoeknees, whos original video of the build is now private. At the moment I'm trying to add rotation to the torso at the waist so I can have rotation in all directions. Basically going for a mech kind of design. I had worked on a bigger model before realizing it was too big for contest submission which had used technic socket and ball bricks to allow for the movement. Creating a gap in the middle that allowed it...