Nooki Nooki Boy first appears in Rubber and the Quest for Diggy the Happy Troll. He flys in front of Rubber, and tells him that the Realm of the Elves is perfectly fine under his protection and his protection alone. If you procede anyway to the Realm of the Elves, Nooki Nooki Boy will challenge you to a fight. He has ranged attacks and stays in the air most of the time. If you win then he will apologize for doubting you, and fly away.
Also, in the game Rubber and the Quest for 1st Prize Trophyman, Nooki Nooki Boy appears as a playable racer.