I think a great idea would be to have custom animations like snow falling on pages and piling up at the bottom of the pages move you mouse over it to make it disappear or when you leave the page or refresh it, little snowman or santa, things like this so you can choose for what you want to customise your pages for what time of year it is.
Easter you could have bunnies or eggs etc animated, promotional animations.
Maybe a page dedicated to quarterly, yearly animations you can set up for what time of year so you can leave the website to update this accordingly without having to change it or remember to.
Be able to import your own animated GIFs easily so that it can appear as you want etc.
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