After reading an article here in Gamasutra, I found it might be usefull for some one to save some of his game performance in case he needs.
Faking a shadow in game engines is not a new topic. But the way itself you use to fake the shadow might be the new topic. As the tutorial is a video tutorial, here listed a quick summary about the method:
1- Pick a piece of animation.
2- Render/draw it from top view as *.png sequence.
3- Build a sprite atlas in your editor.
4- Build a 2d animated sequence for each animation loop.
5- Adjust the shadow transparency, color,.....etc.
6- Add it to the character/object hierarchy.
7- Change the active animated shadow state according to the character current animation state,via code "not in the video".