Mario & the Death Note is a Shame where Mario has to investigate the Kira Killings.
In the beginning of the game Luigi uses the secret name L to investigate the Kira Killings. However Kira(Light Yagami) kills L. So Mario sets out to find out Kira's true name and arrest him with the secret name M while Light Yagami sets out to find M's true name and kill him with his Death Note. Once Mario finds out that Kira is Light Yagami and then Ryuk kills him. Then M kills Misa Amane by stealing his book because he finds out Misa is Princess Peach so that would mean Peach is cheating on him for Light. Mario later becomes a crazy serial killer but that will only be disscussed in the sequel so the creators will make more money.
Mario heard about the recent death of the Angry German Kid and what happened to him, so Mario went and killed Malleo with his new Katsu move. After hearing what happened to his big brother, Weegee telepathicly contacted the German Weegees from inside the German prison and ordered them to find the Katsu Paper where the Katsu spell is located. After they infiltrated Hyrule Castle, stole it and learnt it, they charged at Mario's Mansion. The unsuspecting Mario ordered the Soviet Luigis to attack the intruders. This became known as the Katsu War.
There was a spin-off anime and manga series but didn't have M and L wasn't Luigi. Plus his assistant was some weird kid named Near and he loves to play with toys.