Mini-Mega Hammer

From the Super Mario Wiki

The Mini-Mega Hammer was an item found in Mario Party 4. The hammer would either shrink or enlarge the player who was hit with it, giving them the effect of a Mini Mushroom or a Mega Mushroom. The effect was random. The player holding the hammer could not use the item on himself/herself. The Mini-Mega Hammer is one of Wario's favorite items in the game.

Items from Mario Party 4
Boo's Crystal Ball	Bowser Suit	Chomp Call	Gaddlight	Item Bag	Genie Lamp	Mega Mushroom
Mini-Mega Hammer	Mini Mushroom	Super Mega Mushroom	Super Mini Mushroom	Sparky Sticker	Swap Card	Warp Pipe