Create a more complex rig than in the Beginner Rigging assignment. You can expand the rig from this assignment or create a new rig. Your rig needs to have some of the following techniques:
Inverse Kinematics
Constraints
Limit
Tracking
Transform
Vertex Groups
Bone Layers
Rigging Tips
See the Rigging Tips page for techniques on Weight Painting and using Edit mode to control the vertex groups.