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.

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.