Gravity field

A gravity field 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 gravity fields contain arrows to show the player the gravity direction, as well colors: blue (arrows pointing down), red (or occasionally pink; arrows pointing up), green (arrows pointing the right), gray, and purple (in Super Mario Galaxy and Super Mario Galaxy 2, respectively, arrows pointing to the left). 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 fields 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. The Rightside Down Galaxy and the Upside Dizzy Galaxy feature gravity fields as their main elements. Gravity fields appear only in 2D sidescroller sections of Super Mario Galaxy and Super Mario Galaxy 2, however.

A different variation of gravity fields appear in Toy Time Galaxy. These variations appear as pink walls that Mario (or Luigi) can walk on. There are also occasionally arrow that point to the direction that these walls pull the player towards. These walls also appear green on the Mecha-Bowser planet but otherwise work the same.

Gravity fields return in Super Mario Odyssey, where they appear primarily in the 8-Bit Super Mario Bros.-style mural sections of some kingdoms. Inside the Inverted Pyramid, the player can notice that the arrows on the gravity fields look like murals of the Inverted Pyramid itself, while the ones on the upside down red parts are upside down Inverted Pyramid, thus, looking like normal Pyramids.

Trivia

 * Though not a gravity field, the atmospheric background of the Flipsville Galaxy acts somewhat like one, as it features multiple arrows which reflect the current flow of gravity.