Deut- that depends on if you consider the psycology of the thing. Spirits as manifestations of the psyche... pretty good. Unicorns? If you consider the Unicorn a mistaken identification of a living animal ie. the Oryx (or as the remains of a once living animal ie. the Narwhale) then yes I beleve in unicorns. If you are talking about one of the white horses with a horn on its head, or the variations on that theme through history, then no. Most mythological animals had more to do with metaphore and cultural lessons than most people realize, like the unicorn.
now if your talking about the Cottingly faries for pixies, then no. They are however, a wonderful example of early photographic manipulation.
*bows, grovels and scrapes whilst begging MR Spinkles forgiveness*
wa:do