Ok, well in the Andy's Neighborhood level, when Rex says you can't beat RC in the race without the Rocket Boots, YOU CAN!!!! Ok, first go to RC and he will challenge you to a race. When the race starts run in front of RC, and everytime he tries to get ahead, just stand in front of him and he will stop for a couple of seconds. Keep doing that and avoid the obstacles the entire race to win without the Rocket Boots.
If you just want to get the boss in the level Andy's Room, just follow these steps:
Just exit Andy's Room and head right. Find Rex, and climb the rope above him. Meet the Boss, defeat him, and move on to the rest of the level. As easy as 1,2,3!!
At the main menu, enter Up, Up, Up, Up, Down, Down, Up, Up, Down, Down, Down. A sound conforms the code entry.
First give potato head his ear and get the cosmic shield. Then go to Al's Penthouse. Run into the shield. Then run to the fireplace and get the extra life inside of it. Then exit the level. Re-enter Al's Penthouse and repeat the process to get the extra life as many times as you want.