Legendary creatures play important roles in many ancient texts.
Sometimes they are symbols of the hermetic processes of alchemy;
in other cases they crop up in antique accounts of natural history.
No doubt, these beings haunt our dreams and nightmares to this day.
These are some of the books on dragons, were-wolves, unicorns, mermaids,
giants and other elusive creatures at this site.
Abominable Snowmen: Legend Come to Life
by Ivan T. Sanderson 
The Bigfoot researchers' Bible, by the writer who coined the term cryptozoology.
The Book of Were-Wolves
by Sabine Baring-Gould. 
All killer, some filler.
The Unicorn: A Mythological Investigation
by Robert Brown 
Explore the deep mythological significance of the unicorn.
by Charles Gould 
Dragons, Sea-serpents, Unicorns: fact or fiction?
The Seven Tablets of Creation
by L.W. King 
The Babylonian creation saga, including the battle between Marduk and Tiamat, a very angry goddess taking the form of a dragon.
Fictitious and Symbolic Creatures in Art
by John Vinycomb 
Lore of the fantastic beasts of English Heraldry.
The Celtic Dragon Myth
by J. F. Campbell and George Henderson 
The ur-myth of the struggle with the dragon, told in fine Celtic form with giants, mermaids and sidhe. (English and Gaelic)
The Evolution of the Dragon
by Grafton Elliot Smith 
The dragon: a neolithic symbol of the goddess, mutating into the prototype of the devil.
Dragons and Dragon Lore
By Ernest Ingersoll  [EY]
Lore of the Unicorn
by Odell Shepard  [EY]
What is the reality of the myth of the unicorn?
Also at this site
There is extensive material on Vampires on the Gothic page.
Apocrypha: Bel and the Dragon.
A Legend of Knockmany,
by William Carleton
in Fairy and Folk Tales of the Irish Peasantry, ed. W. B. Yeats 
The raucous adventures of the Irish Giant, Fin-m'Coul.
from Wonder Tales from Scottish Myth and Legend by Donald Alexander Mackenzie 
Scottish tales of Mermaids.