I spy goodbye

[frindle2]

Hello. Would you please tell me what "I Spy Goodbye" means in the context below?

(Vally and Pearl are brother and sister. They wanted to have a game with a wicked magician to get back their father.)

In a desperate effort to keep him on the hook, Vally said, "It can be any game you like."
"Any game I like?" He said it as if each word was uniquely delicious. "How about Race Around the World? Or I Spy Goodbye? Or we could play a little game I call..."
He leaned in towards them, the medallion in his open palm. "Pearl and Valentine Disappear Forever."

Source: The Grandest Bookshop in the World by Amelia Mellor

 

[Skrej]

I think it's reference to the children's guessing game "I spy". Instead of stating an actual object to guess, he's using the phrase as a way of suggesting he wants to leave or get rid of the other people.