This page explains in detail the interactions between the Death Note series and the Mario series.
Death Note chapter Handstand[]
July 2, 2004
Death Note
Mario
In a scene in the sixteenth chapter of Death Note, included in the second volume of the manga, Riuk asks Light to play Mario Golf, but he refuses. He also says that they "haven't played in a while", suggesting that they've been playing for some time. Since it's unknown what console does Light have, it's unknown what game they're actually talking about, it may either be Mario Golf 64, Mario Golf GB or Mario Golf: Tadstool Tour. Mario Golf: Advance Tour was released shortly before this comic was published, so it couldn't be referenced since the comic is written and drawn many months earlier.
License[]
The creators of Death Note didn't have any right over Nintendo's Mario, but they only included a minor reference to the series.