Yume Kojo: Doki Doki Panic
July 10, 1987
Yume Kojo: Doki Doki Panic was developed by Nintendo, and specifically Mario creator Shigeru Miyamoto, so as little nods to his games, Doki Doki Panic features POW Blocks and Starmen, elements originally from the Mario series.
The game was also promoted focusing on the crossover nature of this game, since commercials and advertisements featured an artwork showing Mario and Imajin, the game's protagonist, shaking hands.
Additionally, the promotional telephone Card for Yume Kojo: Doki Doki Panic features images of Mario, Imajin, Peach and Lina on it.
Super Mario Bros. 2
October 09, 1988
The american and european Super Mario Bros. 2, later released in Japan as Super Mario USA, is a clone of Doki Doki Panic, featuring some differences, mainly in the game's selectable characters, changed from Imajin, Mama, Lina and Papa, to Mario, Luigi, Peach and Toad. Most of the game was left unchanged though, making this a type 1 link, since most enemies from the original game became an actual part of Mario's universe, most notably Shy Guys, Bob-Ombs and Birdo, that also appeared in many later Mario games.
Paper Mario: Color Splash
October 07, 2016
At one point during Birdo's concert in Plum Park, she sings "Two hearts in a doki doki panic". This is a reference to her debut in Yume Kojo: Doki Doki Panic.
The game Yume Kojo: Doki Doki Panic was developed by Mario's company Nintendo, so they were able to include elements from the Mario series.
While Fuji TV owned the rights on Imajin and the other protagonists of the game, Nintendo owned the rights on all original elements in the game, so they could use them in Mario games.