To get the most out of this tutorial, you should be familiar with:

point_direction()
image_angle

Let's say you've got a pig throwing some mud. Click around the game window to test it out.

The mud gets flung towards the mouse and falls due to gravity. Cool!

...but the mud just always points to the right! That looks a little funky. Wouldn't it be nice to have it look like the mud is facing the direction it's moving?

Let's see how things are set up, then make a simple improvement using image_angle and point_direction.

obj_mud's CREATE event:

direction = point_direction(x,y,mouse_x,mouse_y);
speed = 40;
gravity = 1;

How do we get the mud to "turn" to face it's path? It's pretty easy. We'll use the built-in variable called image_angle. When you set the value, the sprite will point in a different direction!

obj_mud's END STEP event:

image_angle = point_direction(xprevious, yprevious, x, y);

xprevious and yprevious are also built-in variables store where our arrow was the last game frame. We use those variables to point the arrow's image_angle from its previous position to it's current one, and that's all there is to it.

You can play the improved version here:

Also, you can save the images below and use them yourself!

Turn a Projectile Along Its Path