When starting the game, Momma Hogg will say "We should get a casino in the hotel". Go to City Hall and go to the man with the blonde hair. Select "Build rooms" on the touch screen and find the casino, then go back to the hotel. You will see Tristan Legend (the man who builds rooms in the hotel). When he takes you in the casino, you will talk before it shakes. When you go back in the hotel lobby you will see it. Go outside of the hotel to find a man who will sell you a water gun(250 Simoleons) to make the alien go away. Buy it and shoot the alien with water to make it go away.