Gravity field

Gravity Walls are basically walls that can control gravity, making it go in the direction it's pointing in. Gravity Walls appear in Super Mario Galaxy, in a few galaxies, such Bowser's Dark Matter Plant. The direction of some walls can be changed (and therefore, the gravity) by a Gravity Arrow.

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.