Nice, a Car form :O
Anyways, back to topic, do you want the druid to gain XP when in bear or cat form just like a normal hero or do you want it to be a non-hero unit?
If you want it to be a hero unit then:
1) Make a copy of the hero in the object editor, change the model, icon, sound to whatever you want it.
2) Make a new ability based on any of the transforming abilities like Metamorphosis, Chemical Rage or Bear Form and change the Data fields to whatever suits you
BUT, if you want the Hero to be transformed into a non hero unit, then:
1) Make a dummy ability
2) When the hero casts the dummy ability, hide the hero and create the unit where the Hero was when he cast the ability
3) Run around with the unit, and when the unit is supposed to turn back, just remove the unit and unhide the original hero at the position where the unit was.
