Mario & Luigi: Partners in Time

Mario

Princess Peach

Yoshi

Bowser

Baby Bowser (voice) (uncredited)

There are two Hammer Bros. that at certain point in the game speaks entirely in Leetspeak. When they are defeated, they say "Who talks like that?"

Toadsworth the Younger's line, "You will save her, won't you? I assure you, she's NOT in another castle or anything." is a reference to Toad's famous line in Super Mario Bros.

Fawful, (from Mario & Luigi: Superstar Saga), who was sidekick to the villainess Cackletta, works as a merchant in a shop below Peach's Castle, selling badges in return for beans.