Buffy is in the sense that Tannen is defining tricksters, which I'm not sure I'm completely buying. However, Trickster is a rather complex (and fascinating) mythos: creator/destroyer, persecutor/teacher. A whole series of opposites in one package. For a good and well-written overview article on tricksters, I'd suggest Terri Windling's article:

http://www.endicott-studio.com/rdrm/rrtricksters1.html

(Also has lovely artwork.)