Можно полегче с image_xscale и image_yscale.
Пример:
Step:
Код
image_xscale += 1;
image_yscale += 1;
if (image_xscale == 10 && image_yscale == 10 || image_xscale >= 10 && image_yscale >= 10) {
image_xscale += 10;
image_yscale += 10;
} else if (image_xscale == 30 && image_yscale == 30 || image_xscale >= 30 && image_yscale >= 30) {
image_xscale += 20;
image_yscale += 20;
} else if (image_xscale == 50 && image_yscale == 50 || image_xscale >= 50 && image_yscale >= 50) {
image_xscale = 50;
image_yscale = 50;
image_xscale -= 20;
image_yscale -= 20;
} else if (image_xscale == 30 && image_yscale == 30 || image_xscale >= 30 && image_yscale >= 30) {
image_xscale = 30;
image_yscale = 30;
image_xscale -= 10;
image_yscale -= 10;
} else if (image_xscale == 10 && image_yscale == 10 || image_xscale >= 10 && image_yscale >= 10) {
image_xscale = 10;
image_yscale = 10;
image_xscale -= 10;
image_yscale -= 10;
}