On and Off Barrel
From the Super Mario Wiki
On and Off Barrels are a type of barrels found in Donkey Kong Country. They appear as floating barrels with either the word "ON" or "OFF" written on them.
These barrels only appear in one level, Loopy Lights. The barrel acts as a light switch, lighting up the area when set to "ON" and darkening the area when set to "OFF". Jumping at a barrel will make it switch between the two modes. With the lights off, enemies and the level become harder to see. Stop and Go Barrels from the same game work similarly to On and Off Barrels. When turned on, the barrel lights up the area for a few seconds, and then turns itself off again.
Numerous barrels that function just like On and Off Barrels from Donkey Kong Country appear in Glimmer's Galleon, a pitch-dark underwater stage from Donkey Kong Land 2. However, instead of the words "ON" or "OFF", they display a small light bulb icon. Once touched, the barrels will light up the area temporarily.