From the Super Mario Wiki
The Blizzard Shot is an Offensive Power Shot that Clay and Ace can use in Mario Tennis: Power Tour. It requires L6 Speed, L6 Response and L7 Spin to be unlocked for Clay and Ace. In the story mode, it is used by Elroy. When activated, the user spins towards the ball while the background turns into ice. The user will then hit the ball into the opposing side of the court. Returners of this shot will be pushed back in an ice cube, temporally unable to move.
"A shot that freezes opponents in a bitter-cold flurry."