Ken Wilber describes 3-2-1 shadow work as an essence of certain therapies where you describe someone you very like or dislike in third-person language, then you talk to him/her as a second person, gradually shifting your perspective to his/her consciousness and then you take his/her perspective as your own first-person perspective.
Thus, the dissociated quality or energy of that personality or process or event gets reintegrated within the self-system. It does not mean you really become a monster, say, from your dream, but you rediscover hidden positive qualities beneath the monster apparition. This can be done not only to other people but to deeper potentialities of yourself.
Perspective-taking is an essential component of Wilber's Integral Metatheory and Practice. In his book Integral Spirituality he speaks about Integral perspectivism, and basically what you can do is apply mindfulness to any sort of perspective (and the entire Universe consists, first and foremost, not of things or processes or systems or holons but of perspectives—including primordial archetypal perspectives of Reality).
Also, a method of Voice Dialogue (as adapted by, e.g., Genpo Roshi in his Big Mind — Big Heart process) can be a good tool, because it allows to give space to a great number of inner voices, including such transcendental and unfabricated dimensions of consciousness-being as Primordial Awareness manifesting as eternal and boundless Big Mind & Big Heart.
To experience this holistic process of self-transformation through Integral Holoscendence Meditation and Integral Therapy sessions, feel free to contact me.