A reasonably simple blog to go with Craig675's blog, please read it first.
Unlocking World 4 To unlock world 4, you must finish the final castle of world 2 as MiniMario.
Infinite lives on world 4-5
To get infinite 1-UPs, go the the first pipe spewing out Bobombs. Clear a way to the ground, but without destroying the left and right edges. Get a koopa shell and throw it into the hole, and leave Mario in a place that keeps the bombs coming out of the pipe. The shell should bounce back and forth endlessly, gaining you a large amount of lives.
Free Toad Houses At the end of each level, if Mario jumps on the flag when the last 2 digits of the remaining time are the same, a Toad house appears at the start of the world.
_99, _88, or _77 on the clock unlocks an orange mushroom house(Mega Mushroom)
_66, _55, or _44 gets you a green mushroom house(1-UPs)
_33, _22, or _11 gets you a red mushroom house(Random item)
Unlimited Toad House Items Simple one this. Complete every level in the game. Including the alternative lettered ones.
Alternative Background Pattern(Lower Screen) Again, Simple. Defeat Bowser and Bowser Jr and rescue Princess Peach in world 8's final castle, and a blue mushroom house appears in world 1. In here, it will cost you 20 star coins to buy a new design, and you can choose from 4 reusable patterns. To unlock the 5th pattern, open every mushroom house in the game.
Play asLuigi I saved my favourite 'til last. To play as Mario's brother, hold L+R+A while selecting a save file.