I love Edain McCoy's Sabbaths, especially because of the correspondences lists in the back of the book... but - the correspondences are pretty weird, when looking at them more closely. "Mythical creatures of Ostara: unicorns, merpeople, dragons, pegasos..." What? Why?
To me unicorns are connected to Beltane, together with the White Deer and goats, especially considering the sexual connotations. (Only a virgin can capture the unicorn, which lays his horn on her lap...)
Merpeople... I don't think about sea when I think of Ostara. To me merpeople are connected to Midsummer and beach. Well... perhaps Beltane...
Dragons, just like other firey mythical beasts, are connected to Imbolc.
Pegasos... Epona, the horse goddess, had two main celebrations; June 13th (old Midsummer) and December 18th (close enough to Midwinter), and I have to say both days suit better to associate with all equines than Ostara. Midsummer for "wild" horses, Midwinter for riders and hunters.
So - what is left? Easter bunny?
No, serpents. Not dragons but worms... also knows as wyrms and wurms - the wingless, not fire breathing giant serpents.
What has this to do with anything?
Elf on the Shelf... It's not an old tradition, but I like it. Copy the construction and sew yourself a bendable doll with a little velcro on hands/paws, and start hiding the little doll around the household, like it was Elf on the Shelf. For Ostara you can make a bird or a bunny that reports to Easter Bunny, and have a surprise egg for the child who finds the little mischievous rascal.
Use the endless list of Elf-on-the-Shelf ideas on-line or harmless, kind and nice pranks and practical jokes, like putting some nailpolish on soap, as inspiration of what your shelf-sitter doll could do.
Now... perhaps it's a bit much to have 8 pranksters visiting your home every year, but... I kind of like it :-D