You may wish to use a custom Magic Activation animation for certain spells. After all, having the same mystic star appear every time could get boring!
To change it, you first need to create a Custom Effect in the Animation Editor:
From the top menu, click Animations.
A window titled Animations will open. In it, click on Original Effects.
Another window, this one titled Motion Settings, will open. Enter a name and click on the box under "Effect" to select the animation.