Murphy is a leprechun in the Super Mario Bros. Super Show in Mighty McMario & the Pot of Gold. He made luck happen, however after King Koopa stole his pot of gold he made unlucky things happen.
Everytime Mario, Luigi, Toad and Princess Toadstool were around him bad things happened, and he was sad. Mario and the gang tried to get the pot of gold back however since Murphy was around bad things kept happening.
Mario thought of a plan-being King Koopa's best friend. After Murphy started hugging King Koopa, bad things happened to King Koopa! Murphy got his pot of gold back.
Mario was also accidentally called Murphy by the Puni Elder in Paper Mario: The Thousand Year Door.