Gravity field

A Gravity Wall is a special type of wall that appears in Super Mario Galaxy and Super Mario Galaxy 2. It has the power to control the direction that Gravity pulls Mario within its expanse. The direction in which the Gravity Wall will pull Mario (or Luigi) once its range is entered is specified by painted arrows in a multitude of different colors that appear on the wall behind the character, the most prominent of which are blue, red , 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, either character is immediately pulled towards the object that the arrows are pointing to. The direction that the arrows are pointing on the wall (and therefore the direction of gravity itself) can sometimes be changed if the player finds a Gravity Arrow and spins it or hits it with a Star Bit. Gravity Walls appear in many levels, the most prominent of which is Bowser's Dark Matter Plant, where they act as the main obstacle of the level. Many of them also appear in the Upside Dizzy Galaxy, which was named after and centers around the theme of changing gravities many times.

Trivia

 * It should be noted that Gravity Walls only ever appear in sections of Super Mario Galaxy and Super Mario Galaxy 2 that are played in 2-D sidescroller format, as they would essentially be ineffective otherwise.
 * Though not a Gravity Wall, the atmospheric background of the Flipsville Galaxy acts somewhat like one, as it features multiple arrows which reflect the current flow of gravity.