Pot of Gold Coins
Unlike ordinary coins, the coins in this pot are magical and grant Murphy with good luck as long as they are in a safe place. Should the gold coins get lost or stolen, Murphy's good luck instead turns bad until the pot is retrieved.
In "Mighty McMario and the Pot of Gold", King O'Koopa steals the Pot of Gold Coins from Murphy, turning the leprechaun into a jinx. On top of that, Murphy's bad luck triggers a rain storm that slowly starts to flood his home of the Shamrock Kingdom.
Mario and his friends attempt to take back the coins from King O'Koopa, but Murphy's interference triggers enough bad luck to get them all caught. Eventually, Mario finds a way to use Murphy's bad luck against King O'Koopa, and they succeed in defeating him. Murphy then gets his Pot of Gold Coins back, which in turn brings back his good luck and ends the rain. Murphy's reunited luck even causes Mario to literally drop in on lunch.