Plus and Minus Barrels
From the Super Mario Wiki
Plus and Minus Barrels (also called + and - Barrels in an issue of Nintendo Power) are barrels that can affect the amount of time on a timer. They make an appearance in only one level in the game, Donkey Kong Country 2: Diddy's Kong Quest, which is Haunted Hall.
A Plus Barrel has a green plus sign on it and is used to increase the time on the timer in the level. A Minus Barrel, identified by a red minus sign on its side, decreases the amount of time.
Additionally, a single Plus Barrel can be found at the beginning of "Rickety Race". This Plus Barrel works differently; it speeds up the Kongs' Skull Cart. Similarly, another Plus Barrel is found in one of Haunted Hall's bonus levels, which causes the Skull Cart to travel backwards at a high speed.
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