First off. Malt. Go to the question and answers section. They'll take care of all your billing questions. [;)]
OK, it's a simple idea. Let's have festival specific mobs that only get dusted off and implemented during the time of festivals.
For the Fall Festival: Scarecrows (not strawblights) that have jackolantern heads and straw hats.
For the Winter Festival: Possessed Snowmen. They're based on the oastic model, but instead of the little blob body of the oastic, it's a snowman (complete with tophat). These little guys creep around in the northern climates.
And don't forget Christmas Treants. They look like big walking XMAS trees, complete with blinking lights and decorations. They hit you with Boughs of Holley attacks, or something.
There. Now, what else could we come up with?
(Edit: For the inevitable statement of "there's more important things that need to be done." No. No, there isn't. This idea is the greatest. It totally is. No doubt. And if you don't think so...well, then you'll just have to talk to AA0. It's all his fault. [:D])