If you want to know the general "tactic" behind those fade spells, it generally goes like this:
(1) calculate where the unit is going to go, and calculate the amount of faded "dummies" you'll need
(2) have all of them play their animations, but hide them all (or set their alpha to 0 using the Animation - Set Vertex color)
(3) whenever you display one of the "faded" units, just pause its animation. That way, all the dummies will be at different stages in the animation, synchronized with the caster unit.