The Pack
Buffy Episode Review
In which the Principal gets eaten.
What Happened
Xander is possessed by the spirit of a hyena after a field trip to the zoo. It's when he starts picking on Willow that Buffy becomes convinced that Xander is under some evil influence.
What Did I Think?
The "reasoning" behind Xander's transformation is kept to a bare minimum, so as not to distract from Xander's relationships to Buffy and Willow.
He definitely lets his dark side come out and play. In contrast to the rest of the pack, or to someone like Cordelia, Xander knows enough about Buffy and Willow that he is able to hurt them in very specific ways. His references to how he "feels" for Willow, and comments on Buffy liking her men dangerous are no accident.
Xander is forever dealing with how he acts vs how he is expected to act. In "The Witch" and "Teacher's Pet," he wanted to be manly, strong, confident, and in control. Here, he gets his wish, tapping into that dangerous vibe that Jesse used to attract Cordelia in "Welcome to the Hellmouth." Buffy and Willow, however, do not look only at appearances and words, but also at what motivates them and they are not impressed by the new, "improved" Xander. They want their old, comfortable friend back.
Once again, the main focus on Willow's character is the dimension of her crush on Xander, but this time, the emphasis is on her pain at being ignored as it battles with her fear of rejection. When Xander cruelly taunts her in the hallway, it is basically a dramatization of why she has never made a move.
One character development that is highlighted here is the way Willow never blames Buffy for Xander's crush and his actions regarding those feelings. She is able to realize and understand that even if Buffy weren't in the picture, Xander would still probably not feel the same way about her that he seems to about Buffy. (Something Xander doesn't see so clearly when it comes to Angel.)
When dealing with Xander in his possessed state, Willow shows herself to be quite capable of separating the actions of the possessed Xander from her feelings for her friend, in contrast to how Xander reacted to Jesse's transformation in WTTH. Willow makes a clearer distinction between the two, prompting her to remain strong when he tries to cajole her into setting him free.
In a nice example of continuity, Xander says in "Phases" that he understands the werewolf because of what happened here, and Willow and Buffy have to remind him that he claimed not to remember.