From yeatsvision.com:

• Will ‘or normal ego’ is described, in A Vision A, as ‘feeling that has not become desire because there is no object to desire; a bias… an energy… the first matter of a certain personality-choice’ and, in the words of A Vision B, it ‘has neither emotion, morality nor intellectual interest, but knows how things are done, how windows open and shut, how roads are crossed, everything that we call utility. It seeks its own continuance’, and is an instinct for life and survival.
• Mask is ‘the image of what we wish to become, or of that to which we give our reverence’, or the ‘object of desire or idea of the good’, and it only has meaning if there is the desire of the Will.
• Creative Mind is consciously constructive intellect with memory from before birth of ideal or Platonic forms; it potentially ‘contains all the universals’ and implicitly seeks to understand through generalization but needs materials with which to work and create its order, so that if it were isolated from the other Faculties it would be indiscriminate in its impressions since lacking direction.
• Body of Fate is the internal representation of ‘the physical and mental environment, the changing human body, the stream of Phenomena as this affects a particular individual, all that is forced upon us from without, Time as it affects sensation’; it has greater independent meaning since it is the personal, constituent fragment of the general reality, and ‘the visible world is the sum of the Bodies of Fate of all living things’