The first world of New Super Mario Bros. 3 (Silver-zoroark's version). Very similar to the first world of all the other NSMB games, but this one includes Peach's Castle more and a few Toads have houses there.
World 1-Peach's Castle
The "introduction" to the game. Peach's Castle is set on fire by Lakithunder and Mario has to get to the top. When he does, he finds Lakithunder and makes rainclouds to dowse the fire. Then Mario is free to go.
The first real level to the game. The power-ups are Rodent Leafs. Enemies include Goombas, and Koopa Troopas, and there is grass and blocks everywhere.
A level set underground. It introduces Fire Flowers and Pirahna Plants, and has some pipes and secrets.
A level in the sky. It has lots of mushrooms, and there is a beanstalk and a Mega Mushroom somewhere. There is also a Roulette Block halfway throughout the level.
The first tower of the game. There are Dry Bones and ropes to climb. At the top Mario must fight Bowser Jr. head-on. When he defeats the koopa he saves Toadsworth and two toads. After that Toad Houses open up around the world.
A water level filled with Cheep Cheeps. There is a secret flagpole somewhere in the level leading to a secret level in World 1.
A grass level featuring moving blocks and a Mini Mushroom. There is a secret pipe area and at some point in the level there is no ground.
A level with lots of pipes and Pirahna Plants. Venus Fire Traps are introduced, and at the end of the level there is a sort of a maze.
The first castle in the game. It has lava and Podoboos inside it. The boss is Bowser, spewing fireballs. The fight is a bit harder than in New Super Mario Bros. but not too much.
The enemy course is harder the harder the mode on.
Easy - 4 Goombas, 2 Mini Goombas.
Medium - 2 Big Goombas, 2 Goombas.
Hard - 4 Mega Goombas