Simplify the following text for a Grade 6 native English-speaking person.
Original: Waluigi 's first appearance was in the Mario Tennis games for the Game Boy Color and Nintendo 64 , as Wario 's doubles partner ; he would remain doubles partners with Wario in all later Mario Tennis games . Later , along with Princess Daisy , he joined the Mario Party series ' roster in Mario Party 3 , in which he owns an island full of explosives .
Simplified: He was made as a partner for Wario in Mario Tennis and other Mario sports games and has no real story behind him .