There are a couple of ways to do this.
Usually, I enable semi-transparency, and then make several different images of 1 image, with less opacity every time, usually in increments of 5 or 10. For example, if I want the body to fade in and out of transparency, I'll make 11 images;
preset_#body100.png
preset_#body90.png
preset_#body80.png
and so on, with the numbers representing the opacity I've set that specific image to.
Then in the code, I would make the textures animated, meaning switching between all eleven, at a rate in which I can set.
Example;
material preset_#_bodyMatL
{
technique
{
pass
{
depth_check on
depth_write off
scene_blend alpha_blend
texture_unit
{
anim_texture preset_#body100.png preset_#body90.png preset_#body80.png preset_#body70.png preset_#body60.png preset_#body50.png preset_#body40.png preset_#body30.png preset_#body20.png preset_#body10.png preset_#body0.png 0.5
}
}
}
}
material preset_#_bodyMatR
{
technique
{
pass
{
depth_check on
depth_write off
scene_blend alpha_blend
texture_unit
{
anim_texture preset_#body100.png preset_#body90.png preset_#body80.png preset_#body70.png preset_#body60.png preset_#body50.png preset_#body40.png preset_#body30.png preset_#body20.png preset_#body10.png preset_#body0.png 0.5
}
}
}
}
This code goes through all of my images on the preset's body, making it appear to fade, at a rate of 0.5 seconds per image.
Of course, you can edit this and change it to your needs, maybe only a certain layer of your preset needs this, or whatnot.
But this is just a little something to help you use it.
If you were looking for a different way of doing it, let me know? c: