This action is used to reverse certain values related to direction and movement. The available options are: Reversing direction will simply add 180° to the current direction (looping around 360° if necessary, so, for example, reversing 270° would give you 90°), reversing the horizontal or vertical speed will simply multiply the given speed vector by -1, and choosing gravity will do the same as choosing direction, only for the gravity direction.
Argument Description direction The direction to reverse
The above action block code checks for a collision of the instance with "obj_Wall" relative to the current position to the left and to the right. If one is found then the horizontal speed is reversed.