Invincibility
Here is how to be invincible--first hold down shift and control, 
then you will see a rectangular box on the upper left of the 
screen. Type buzz's laser. Now you are invincible. 

Green laser locations
Green lasers will allow enemies to be killed with a single shot. 
They can be found at the following locations. 

Andy's House: When you go to the garage, find a way to get up to 
the van. When you get to the top, you will see a green laser. 
Andy's Neighborhood: Find your way to the location with a broken 
car. The green laser should be right in front of you. 
Alleys and Gullies: Turn to the right when you see the first 
airplane box. 

Finding Mr. Potato Head's eye
To retrieve Mr. Potato Head's eye (and receive the disc 
launcher), keep climbing up the construction site. You will 
eventually find the eye.