If you do console.log(Game.alienfort) immediately after creating it, you will see the position printed. Note that the position is a string like “5x7” not an object like {x: 5, y: 7}.
So in your code where you say makeMonster(Game.alienfort.x + "," + Game.alienfort.y) you probably want to change it to this: makeMonster(Game.alienfort) because the variable is already in the correct x,y string format.