My content area is biology, and our major biology education research journal recently published a nice overview on this (open-source reference at end). Hopefully the results are relevant for your field as well.
- Make sure content is correct
- Follow instructions (keep to time limit and topic)
- Make the topic relevant (bring in a hot topic from research or news)
- Involve the audience (have an activity or "clicker question")
- Have teaching slides or use the board
I'd recommend trying to find a course (at the interviewing school or at a similar institution) that has an online syllabus so you can see how much is normally covered in a lecture. Then your first slide can be one that shows how you would cover the day's content, but places your 10 min talk in context. This is helpful if the "fun" part you want to do is in the middle of the imaginary lecture.
Then, pick something from the course that you think you can create an activity about. Can the audience develop something? Vote on an aspect of the code? Work in groups to find three common errors in a short piece of code? (I'm flailing around here, as game design is a mystery).
Build your lecture around that activity. Have the activity near the beginning. Plan on everything taking at least twice as long as you think.
Be enthusiastic.
Congratulations on the invite, and good luck!
Smith, M. K., Wenderoth, M. P., & Tyler, M. (2013). The Teaching Demonstration: What Faculty Expect and How to Prepare for This Aspect of the Job Interview. CBE-Life Sciences Education, 12(1), 12-18.