An animated brush is a type of custom brush that contains multiple images.  These images can a series of animation frames that you can use to paint directly into an animation, or simply a group of images like trees or flowers that you would like to paint with.

There are two ways to create a custom brush, each with it's own advantages.  You can use either method freely.

To create an animated brush from an animation, simply hold the Alt key while selecting a custom brush in the normal way.  You should already have an animation created or loaded of coarse.

See the section on custom brushes for more information on picking up a custom brush.

You only have to hold the alt key down when you initially press your mouse button.  After that, you will be in the animated brush pickup mode.  This frees up your hand to scroll through the frames with the arrow keys while using the bounding box, so you can make sure you're picking up the area you want to, and nothing gets clipped out.

When you let up on the mouse button, the application will begin picking up frames from your animation, starting at the current frame, and continuing to the last frame.  When finished, you will have a new animated brush.

The Brush manager will let you build an animated brush image-by-image.  Select the Store / manage item under the brush menu.

Clicking on the 'Add frame' button adds the current brush image to the brush image (or images) that the Brush manager keeps in memory.  You can add as many frames as you like, and as memory permits.  The brush images do not have to be the same size.

The 'Delete frame' button deletes the last image that has been added.

See the section on the Brush manager for more information.

Click the 'Show Filmstrip' button to show your animated brush in a filmstrip format.  You can also keep this window open as you work.

You can paint with an animated brush just like a regular custom brush.  You can even apply the same dynamics and color options to an animated brush.

Clicking the Allow custom brush transforms button on the custom tab will allow all possible transforms to be applied.

You can paint in matte mode, just like a regular brush, making it possible to used an animated brush to create all kinds of natural media tools.

As well as using an animated brush as a painting tool, you can also use it as an animation tool.

Say you picked up an animated brush of a man walking.  You can now draw him walking across the screen by holding down the alt key while you draw.  You have to have an animation initialized in order to do this.

Take note that the Steps setting on the tool panel has an effect on how fast your animated brush will be able to move as you draw with it.

You could also use the stroke player to accomplish the same task, or you could use the brush keyframer.  All of these tools support animated brushes.

The Brush timeline is functionally similar to the animation timeline.  With it, you can add special effect filters to an animated brush, transform it, or change it's transparency.