Input.mousePosition.x
Input.mousePosition.y

var cursorImage : Texture2D; //изображение прицела
var cursorSize  : int = 32; //размер прицела
   
function OnGUI(){ //отображать на экране
         var x : int;
         var y : int;
    if (Input.mousePosition.x > 0 && Input.mousePosition.x < Screen.height && Input.mousePosition.y > 0 && Input.mousePosition.y < Screen.width) {
                 x = Input.mousePosition.x;
                 y = Screen.height - Input.mousePosition.y;
                 }
         else  {
                 x = Screen.width * 0.5;
                 y = Screen.height * 0.5;
         }
         GUI.DrawTexture(Rect(x, y, cursorSize, cursorSize), cursorImage);  
}