From the Super Mario Wiki
The Illusory Save is a Defensive Power Shot that is used in Mario Tennis: Power Tour. It is used by Sheri, who is first played agiants in the Island Open Doubles Final. To obtain the save for the use of Ace and Clay, L4 Jump and L2 Spin are required. Once activated, the user will generate illusions of themselves that spread out to the left and right side of the player, with the one in front of the ball being the real character. Afterwards, the user will weakly return the ball.
"Save the ball with an illusion that spreads out either side."