Luigi, like most SA characters, is a simple and less detailed version of his original character. He is very similar to his brother Mario in appearance, but he instead wears a green shirt and cap, has a only two bumps on his mustache and his taller than Mario due the the irregular shape of his head. (also is his legs longer than Mario, or is Mario just half-crouching all the time)
And also Luigi released mario from the abyss in Luigi's haunted mansion