image_yscale - vertical scaling of a sprite.
image_yscale is a local variable that contains the vertical scaling of a sprite. It is by default 1, which means the sprite is scaled to 100% (its normal size). A value lower than 1 will decrease the size of the sprite and a value higher than 1 will increase it.
image_yscale only scales the sprite vertically (makes it taller). If you want to scale a sprite equally, you must use image_yscale in conjunction with image_xscale.
Example of Use
image_yscale = 2;
This will make a sprite twice as tall.
Keeping Aspect Ratio
To keep the aspect ratio of a sprite, you must use image_yscale with image_xscale.
image_xscale = 0.5; image_yscale = 0.5;
This will make a sprite half its normal size.