This page explains in detail the interactions between the Keroro Gunsō series and the Mario series.
Keroro Gunsō episode Keroro And Natsumi Which Way to Heroes?![]
September 08, 2006
Keroro Gunsō
Mario
In the twenty-third episode of season 3 of the anime (Episode #126), to demonstrate a new "Reality-avoiding" device, Kururu and Saburo transport themselves into a videogame which is clearly based on Super Mario Bros. Also, Kururu is dressed as Mario and Saburo is dressed as Luigi.
License[]
The creators of Keroro Gunsō didn't hold any right over Nintendo's Mario, but they only included a subtle reference to the game.