The Mega Mushroom is an item that only appears in Dry Bones Kart Wii. It is most often acquired in middling positions (4th to 9th place). When players use this item, they grow bigger and their voice gets much deeper. This item offers the players the ability to squash other players for a certain amount of time, reducing their speed and making them lose their items. While this item is active, the players receive a speed boost and cannot slow down when going off-road, and they are invincible to all dangerous things, except for the Star, Bullet Bill and Blooper, giving them the power to destroy any items or any course obstacles, except those that are big and metallic (such as Chain Chomps). If players get hit by Lightning while they are big, they shrink back to normal size rather than becoming tiny. The effect also ends prematurely if players fall off the course. The Mega Mushroom's theme music from New Super Mario Bros. is played for the duration of the item's effect.
The Mega Mushroom was originally going to reappear in Dry Bones Kart 7, but it was scrapped due to incomplete functions. Its codes are still in the game's data. In Dry Bones Kart 8, it doesn't appear as an item at all (but in its port, the item is going to return).