Appearing tonight Polka dots!
Choose Layer>New>Solid or press Cmd+Y (Ctrl+Y).
Select the layer and double click on the Ellipse Tool from the Tools Palette. (If you don't see the Ellipse Tool, hold down the Rectangle Tool to reveal the Ellipse Tool beneath ).
Select the mask and press Cmd+T (Ctrl+T) to access the Free Transform Points Tool. You may need to make the Ellipse more circular.
Press the Shift+Cmd (Shift+Ctrl) to scale the Ellipse to a smaller size from the center of the layer.
Choose Effect>Render>Stroke. Change the Brush Size to a value larger than 10.
Change the Spacing to 100 percent-voila! Pokka Dots!
Animate the Start or End values and watch your dots appear or disappear.