Some of the Boxing Ring Stage titles contain references and easter eggs.

Luigi's, "The Eternal Understudy", is a reference to his unlock screen in the original Super Smash Bros..

Fox's title in the European version "Never Gives Up! Trusts His Instincts!" is a reference to a line in Starfox 64 said by Peppy in the Asteroid Belt level (and later on said by Fox's father).

Kirby's European title "Gritty in Pink" is a reference to the movie "Pretty in Pink".

Sonic's European title "Speed is his Game" is a reference to one his popular quotes "Sonic's the Name, Speed's My Game!".

Pikachu and Jigglypuff's European titles are actually just their Pokedex names.
Contributed by Takahashi2212