Pretty, Unique, and Amusing, but...
I wish you didn't have Sisyphus grunting so much. It got very annoying. I understand you're trying to better illustrate how much strain he has in pushing the boulder and such, but the grunts don't sound right. I mean, imagine how annoying Bitey would be if he constantly made noises like that.
But this is still in my personal top twenty flashes in terms of art and animation.