Sense of Self
When Tim and the party ask Pooka who or what he is, he simply states, "Pooka is Pooka." He explains that he has no sense of self, becuase he does not need it. He is part of a whole, the messenger of the Guardian's will to the Pillar. He is also the mentor and sage for the Pillar. But he has no "self" because he does not need one. He realizes that humans need something more to understand, so he explains that he is the sub-spirit sent to help the pillar (Tim) and his bodyguards (Ashley, Brad, and Lilka) get through the Pillar trial. Throughout the course of the game, Pooka and Tim talk. Pooka does not acquire a real sense of self. He is always and forever will be Pooka. But what is Pooka?
Pooka is Pooka!
Pooka's sense of self (or lack there of) creates an interesting character. Pooka does have a "self" he just has not realized that it is changed through his interactions with Tim. Although Pooka follows the will of the Gaurdians he is also required to follow the will of the Pillar. In the past, these two wills were interchangeable. They had the exact same goal. Tim is stubborn and for his part wants to follow the Guardians will and save the world - just on his own terms. When the Guardians get upset at Tim about this, Pooka takes Tim's side reassuring the Guardians that he will help Tim find an answer that will please the Guardians. I believe that if Pooka truly had no sense of self, he would not go along with Tim. He would merely do as he was told based in what the Guardians instructed. However, just because Pooka makes the decision to support Tim does not mean that Pooka knows he has developed a sense of self. And he does, because he wants to be with Tim and support him - a decision he makes in Reypoint Wing.