In this mission, Nero must execute mid-Air Buster five times in a row without touching the ground.
Go to the center of the watered area, jump, then Air Hike (if obtained) and then Snatch, Buster, Snatch, Buster, etc. If the scarecrow seems too far, try changing target. After you successfully execute the mission, kill all the remaining enemies and get the blue orb fragment.
Alternatively, you can choose to play it in Automatic Mode as Nero and just need to keep tapping (Default) in mid-air.
An Alley-oop is a play in Basketball where a player throws the ball high in the net and the teammate catches it and scores usually by a dunk.