I was a mascot in high school (I went to two schools, I was Admiral Farragut at one and a big blue furry bird thing at the other) and while I'm sure it's different, the main requirement was being enthusiastic. If you can dance, that's good too (I could not.)
It can be a fair amount of work, since you're running around in a big costume, but is definitely a good time. Everybody is happy to see you, kids like you, and ladies love you. Ok, maybe that one is a stretch.
One of my buddies actually used to be the turtle at UMd, which just goes to show that sometimes good things can come from College Park.
Here's the flyer from GW. Sign up! Click it for the full version!