He's not jumping. He's so infused with the power of WAAAGH that gravity has ceased to affect him. There should be grots holding chains holding him down, I think.
Nice so far, HC. My ork-playing buddy and I were talking about making him but never got around to it. One thing we did experiment with, is taking thin metal wire, attaching it in random places and painting it blue with white highlights, as a lightning effect. We didn't use it for old Zaggy, but we did end up using it for his Eldrad and it worked suprisingly well. Just put a whole bunch of kinks in it, make it fork in appropriate places...
I love weirdboys. For anyone who doesn't know the fluff, all ork power (including their technology) is solely based on how hard they believe it will work. Weirdboys are so infused with the psychic belief, that they can channel it into extremely destructive bursts at the enemy.
Except when they make the heads of every nearby ork explode.
WAAAAAAAGH!