mythical means told in stories
If you mean Griffins, no they are not. They are mythical creatures.
It's poseidia. The capital of the mythical Atlantia.
Mythical is a make believe creature.
If you mean Sasquatch, it is a mythical ape like creature said to be in North America.
If you mean Medusa - she was a mythical woman who had snakes on her head instead of hair.
A dragonslayer slays dragons. Like anything else, some are better than others. However, only a mythical personage can slay a mythical creature.
Again, context is key: If you were to say that a certain book was the author's first mythical work, it would mean that the book in question was that author's initial fictional offering.
Fairies are mythical creatures and do not exist in real life. They are a part of folklore and fairy tales.
a mythical food
okappa bobbed hair (from resemblance to the mythical Kappa's hair style)
a fable means a made up tale with mythical creatures in it
A sphinx is a mythical creature with the head of a human and the body of a lion.