Adding a screen overlay (ie snow, bats, hearts, etc)

I would like to see an added animated screen overlay to add effects to the screen/layouts to add a bit more *pop* to the screen. For example, a "light snow" effect over the full screen or more preferably a controllable portion of the screen for the month of december for the holidays. The snow would float down and around, maybe small bats and ghosts for october would fly and float, and hearts and cupid might do the same. I've tried using the apps and tricks I have learned so far, but the one video limit is something i haven't managed to work around yet.