obj_player:

Step:

image_xscale = obj_player_arm.image_yscale

Keyboard Left:

x -= 3

Keyboard right:

x += 3

obj_player_arm:

Step:

direction=point_direction(x,y,mouse_x,mouse_y)
image_angle=direction
x= obj_player.x
y= obj_player.y

if direction>270
{
  image_yscale=1
}
if direction<=90
{
  image_yscale=1
}
if direction>90 and direction<=270
{
  image_yscale=-1
}
//this is the main code
//
//it tells the sprite to flip on the y axis when it reaches a cretain direction

Global Left Pressed:

instance_create(x,y,obj_bullet)

Draw:

draw_sprite_ext(sprite_index,image_index,obj_player.x,obj_player.y,image_xscale,image_yscale,image_angle,c_white,1)

obj_bullet:

move_towards_point(mouse_x,mouse_y,10)