Bonus Arena:
 
In World 1 Arena 1, after you have blown up the
atomic door with the "world's smallest atomic
device", turn around and go back to the original
cave you started the game in. You will find a 
shimmering pink ball. Step into the ball. You 
will appear in a new arena. Shoot all the Grunts
in this arena. A tornado (useful for killing 
everything in an arena) and health bites will 
float down. Pick up these goodies and then
step back into the ball. You will arrive back 
into the original cave and continue onward to
Arena 2.