im not sure if it is possible to create this effect with jass. However i have seen it done in a spell pack i downloaded from here. basically it creates the effect that the unit is standing on its head. perhaps the person who made the spell used a customized model. Ill see if i can find the spell.
I did never find (or seek) a way to rotate a unit via JASS... But if you want it to be fixed in a certain state of rotation, modify the value "orientInterp" in the object editor. Try negative values. (possible by holding "Shift" while clicking on it)
HAH! ok I figured it out. By changing the units model size via triggers to -100% I was able to make the unit stand upside down. However, he runs backwards (lol) any suggestions?
(Heres a copy of the trigger I made) Rotate Events Player - Player 1 (Red) types a chat message containing rotate as An exact match Conditions Actions Animation - Change Gryphon Rider 0002 <gen>'s size to ((0.00 - 100.00)%, (0.00 - 100.00)%, (0.00 - 100.00)%) of its original size
(I had to use 0-100 because world editor wont let you imput a negetive integer in this trigger (even with it allowed under preferences))