Invincible and Level Skip
During the intro press Down A Up B Left Right B A B A B A Up Down. Plus during gameplay press Select to skip levels.
Flag Waving Sam
Go to Level 1. When you find a strange animal called Rees-Tartah,activate it. It should wave a flag. Move Sam right next to Rees-Tartah and make their right hands match.If you have Sam in just the right spot, it looks like Sam is waving a flag. This is just for fun, so don't expect Level Select or anything.