Gold Boo

Gold Boos are golden variants of Boos.

New Super Mario Bros. 2
Gold Boos first appear in New Super Mario Bros. 2 when Mario or Luigi touch a Gold Ring. They begin to flee upon turning gold, leaving a trail of coins behind for the player to pick up. Just like all the other golden enemies, they give five coins to the player upon defeat. Big Boos also have the same effect and turn into Gold Big Boos.

Paper Mario: Sticker Star
A Gold Boo appears in Paper Mario: Sticker Star in the Mansion Safe in The Enigmansion, where it acts identically to a regular Boo, but drops twelve coins after the battle.

Mario & Luigi: Superstar Saga + Bowser's Minions
In Mario & Luigi: Superstar Saga + Bowser's Minions, a gold variant of Captain Boo is unlocked whenever the Boo amiibo is scanned in the Minion Quest: The Search for Bowser mode.

Mario & Luigi: Bowser's Inside Story + Bowser Jr.'s Journey
In Mario & Luigi: Bowser's Inside Story + Bowser Jr.'s Journey, a figure of Gold Boo appear in the Tower of Yikk's office, among with the Boo figures like Boo, Big Boo, Tail Boo and Bomb Boo, unlike the original game.