This is a grappling related question. As a 10th level druid, would it be possible to wild shape into a Huge animal, cast Animal growth on yourself thus going to Gargantuan then be further pushed to Colossal (not in terms of size but strictly for CMB) by way of Powerful Shape? I would imagine this would make the druid quite effective a grappler.
Unfortunately, it's not possible
The supernatural ability wild shape is an effect like that of the spells beast shape et al. of the transmutation subschool polymorph and "other spells that change your size have no effect on you while you are under the effects of a polymorph spell."
Further, the spells beast shape et al. on which the supernatural ability wild shape is based don't change the caster's type. Unless the druid possessed the type animal to begin with, the druid, despite having the form of an animal, still can't target himself with a spell like animal growth because of the spell's entry Target: One animal (Gargantuan or smaller).
The feat Powerful Shape changes neither of these restrictions.