When you play the Megaton Punch mini-game in Kirby's Super Star you can spot some familiar faces in the crowd. On both the far most right and far left side of the crowd: Mario, Luigi Toad and Birdo can be spotted.
 
Belive it or not but our beloved plumber has managed to sneak into yet another part of this Kirby game. When Kirby gets the Stone Ability (i.e. he swallows a rock or stone enemy) he can turn into one of many different stoneshapes. One - very rare - shape is Mario making the classical Peacesign... So now you know that.