Okay for the great design of the Mystery Buttons. But what happens if you want to use a clip of your own ?
Let's imagine you've prepared two clips :
One clip for the Up state (MyClip_out)
One clip for the Over state (MyClip_over)
Caution : for the convenience of this tutorial, those clip are presented in a loop. If you plan to use them in
a mystery button, you'll have to insert a STOP command at the end of each animation.
First, open the Mystery library.
Drag and drop the Mystery Button of your choice
(we choose the BTM_glassball button)
As usual, double-click the button to access its layers in the TimeLine.
We're going to exchange the clips in the two states of the button. Select the first Key in the graphic layer and click on the button on the scene.
In the properties panel, click the swap button.
Choose the clip you designed for the UP state. Double-click it or click OK.
If your clip is not the same size as the original, choose the free transform tool to resize and move your clip under the dotted ghost of the Mystery component.
Repeat the processus for the OVER state of the button, swapping the original clip with your own one.
Don't forget of course to edit the Parameters of the component to change the text, its color, etc...
to resize and move your clip under the dotted ghost of the Mystery component. 
