This is a servo driven animatronic skull that I've been working on.
Requires 4 standard servos and 5 micro servos (9g HXT900 to be exact). Open/close jaw servo should be extra fast for the best look.
ball links for neck:
Other hardware/software suggestions:
Lynxmotion Ssc‑32u - servo controller
Visual Show Automation (VSA) - animatronic software