A green candle.
The Green candle only exists in Extra mode.
It is stuck on The Greenery on the 5th Floor. To get it down you have to obtain the Stick from the Elderly Tree. Once you have it you have to lit it with the Candle on the night desk beside the bed in the yellow flower room.
Once the green candle is lit you use it to burn the rope on the birdcage in order to get the bird out, the bird won't fly out of the cage right away so you have to scare the bird with the green candle. Once the bird is out, it will eat The Greenery and you can make progress in the game.
When the Garden has turned red then if you interact with the candle, you will get caught on fire and burn. Game Over.