What is the name of the group of welsh myths/legends

What does cole think are the ingredients of his “cake”?

What is implied in this sentence from mark twain's "the £1,000,000 bank-note"? i was puzzled, and wanted to discuss the matter a little further, but they didn't; so i took my leave, feeling hurt and insulted to be made the butt of what was apparently some kind of a practical joke, and yet obliged to put up with it, not being in circumstances to resent affronts from rich and strong folk.

How does shakespeare transform the myth of phoebus and daphne to dramatize this theme?