The biggest bust in Yankees history was 7 feet tall, made $40 every home game and spent most of his brief career in the upper deck.

From 1979 to 1981, the Yankees employed a mascot named Dandy. He was big and blue and a spectacular failure—a historical oddity for a proud franchise that has collected 27 world championships but would just as soon forget he even existed. Which, to be fair, isn't terribly difficult to do.

"It's one of the sadder stories," said Wayde Harrison, who created Dandy with his wife, Bonnie Erickson.

For Mr. Harrison and Ms. Erickson, who run their business, Acme Mascots, out of their apartment in Brooklyn Heights, the Dandy saga is all about bad luck and lost opportunity. And it resonates this week with the Philadelphia Phillies visiting Yankee Stadium for an interleague series.

In 1979, the Yankees appeared eager to replicate the success of the Phillie Phanatic, the green, pot-bellied mascot that Mr. Harrison and Ms. Erickson created in 1978. In his first two years of existence, according to Mr. Harrison, Phanatic-related products generated $2 million in revenue—and his popularity has not waned.