The skits more often effective are those that compact a number of music clips together, showing diversity in flavor, speed, emotions, etc. Mix 15-30 seconds of song clips that you can perform from. Show lots of energy and lots of positive gestures. None of us have all the answers, but we may have some tips that we can share with the beginning character performer concerning trying out and getting a job. Find out what the old mascots did, and copy some of their best schtick.
Some schools require pushups after each touchdown.
Try and talk to some of the cheerleaders. See if there is anything they know the cheerleading coach liked to see the mascot do. While you're at it, see if any cheerleaders might be willing to tell you what kinds of cheerleading partner stunts they've seen mascots do. Even a small stunt can be impressive in a tryout. These are a few of their favorite things, but just the basics.