Willy

Willy Costello is a character in Mario Tennis: Power Tour who hails from Factory. He is Clay's or Ace's final opponent in the Island Open singles tournament, defeating last year's champion, Dweezil, to make the semifinals and Mynx to make the finals. In the doubles tournament, he and his doubles partner, Sheri, defeat Elroy and Tori to make it to the finals against Clay and Ace.

He is also the younger brother of A. Coz and B. Coz, both of whom trained him. In a form of revenge, A. Coz and B. Coz trained him in hopes of him besting Alex's student--the player. Just like his brothers, Willy is a rookie who no one expected to get very far. During the tournament, when talked to, he expresses more interest in a good challenge than a victory. At the Singles final, he says that Clay/Ace and him were lucky to be at the Island Open and been enjoying the match. Willy even suggests that since the both are new to just have a good time as if nothing were at stake.

Willy's Offensive Power Shot is the Summoner Shot and his Defensive Power Shot is the Hand-Power Save.