Examples
You can gain some inspiration and ideas by watching other people's work. In the past three years, students in Dr. Anurag Purwar's Freshman Design Innovation class at Stony Brook University have created hundreds of robots using SnappyXO and mechatronics kit provided to you.
You can go to http://www.youtube.com and search for MEC101 Stony Brook and you will find hundreds of video demos of the robots that students have created in the past. Take a look at them to gain some inspiration, but definitely not copy them. Use your own imagination and creativity. However, not all of them qualify to be a valid idea for this challenge.
There are a lot of other interesting robots and mechanisms on display at youtube.com. Search for robots, mechanisms, kinematics as key words. Complexity could be widely varying. You should pick something that provides the right balance.