You control another nontoken creature with mana value 2 or less.
Steps
Cast Cavern Harpy by paying its mana cost.
Bygone Bishop triggers twice, creating two Clue, two Food and two Treasure tokens.
When Cavern Harpy enters the battlefield, it triggers twice, returning itself and another creature with mana value 2 or less from the battlefield to your hand.
Activate the two Treasures by tapping and sacrificing them, adding two mana of any color(s).
Cast the other creature by paying its mana cost.
Bygone Bishop triggers twice, creating two Clue, two Food and two Treasure tokens.
Activate the two Treasures by tapping and sacrificing them, adding two mana of any color(s).