When you get beyond a gold medal in Solo or Co-op modes, little gems will appear around your gold medal and "Wow!" or "Great!" will appear. Obtaining all of these is a hard challenge, but with no rewards.
On the heroic levels in the evil lair, hit the big robot that appears in most of the levels. This causes him to shoot four rockets in the direction he was facing when you hit him. This is useful for getting the gold medal.
To display the cheat menu, press UP, RIGHT, DOWN, LEFT at the title screen (where you normally press A and B). Unlock the following cheat options by entering the corresponding codes:
CHEAT OPTION - CHEAT CODE Everything Unlocked - Nothing But Hope Turn on Blox time - Freeze Frame All Colored Blox - Rainbow Blox 1 million Boom Bux - Bailout All sound effects are Virus Blox sound effects - Musical Fruit All animations turn into flowers - Blox Bouquet