You find a midpoint between source and target and form the ellipse there. Its width is then equal to half the distance while the height is smaller than the width (otherwise it is circle or looks funny). Rotate it so that it faces either the source or target point (as it is an ellipse it does not mater as both have same results). Finally use a1 to control the movement around the ellipse, going from 0 to 2pi will signify a full rotation around the ellipse. You may need to offset a1 initially to start at an appropriate location.
Thanks a lot, Spartipilo. What I want is to make a spell and looks like this:
1. the hero cast the spell --- warstomp.
2. at the same time, create a dummy to cast warstomp at a random location in 500 range of the hero.
3. repeat "step 2" every 0.5 sec for a duration of 3 seconds.
Thank you very much for your compliments and sorry for freaking out. But I myself reckon that if the speed change isn't that significant and the spent effort is not worth it, please focus on other systems for the map instead. Thank you once again and good luck.