Gravity field

A Gravity Wall is a special wall that appeared only in Super Mario Galaxy and has the power to control all. The walls with the arrows on them have the power to control Gravity in an area which is specified by painted arrows in four different colors that appear on the wall behind the character (Blue, Purple, Green and Gray). The effect of Gravity Walls is such that as soon as Mario or Luigi enters the area with the painted arrows and colored background, that character is sucked towards the object that the arrows are pointing towards.

Gravity walls appear in many levels, the most prominent being Bowser's Dark Matter Plant where they are the main difficulty of the level. Many other levels have them sucking the player to a gooey doom. The direction of the arrows pointing towards the wall (and therefore the direction of the gravity itself) can also be changed if the player spins a Gravity Arrow or hits it with a Star Bit.

Blue Walls
A Blue Wall makes the force of gravity pull Mario downward.

Purple Wall
A Purple Wall makes the force of gravity pull Mario upward.

Green Wall
A Green Wall makes the force of gravity pull Mario from the right.

Gray Wall
A Gray Wall makes the force of gravity pull Mario from the left.