Gaddlight

The Gaddlight is an item used in Mario Party 4. When an opponent sends a Boo (from a Boo's Crystal Ball) to steal coins or a Star, the targeted player can automatically use it to flash light at the Boo, scaring it away (making the opponent unable to steal Coins or a Star from them). It serves the same function as the Boo Repellent from Mario Party 3. The Gaddlight can be thrown away to free up space in the player's inventory, though this counts as the player using an item on that turn. On Boo's Haunted Bash when a player lands on a Happening Space and summons the Big Boo, when the Big Boo steals coins or stars from the other players, this item for chasing the Boo away does not work for the Big Boo.

The item's name seems to indicate that it was invented by Professor Elvin Gadd, although a symbol of his head (seen on most of his inventions) is absent from the item.