Clear Skies is the 4th World of Ultra and Super Duper Mario Bros. (or Super Duper Mario Bros. Ultra). This World is featured in the sky, introducing Lakitus and Spinies to the game. It is the 2nd World to have a Castle as the ending level.
Level 4-1 - Grass
This level is the first to feature Lakitus, throwing Spinies at the player(s) through the entire level. The only other enemies are Pirahna Plants and Kittkits, (the Kittkits help defeat Spinies) and the power-up is a Bunny Suit.
Level 4-2 - Under-Ground
Another underground level. It has lots of platforms and introduces Buzzy Beetles, crawling on the many platforms in the level. Inky Pirahna Plants re-appear as well as other types of Pirahna Plants, and the power-up is the Skate Baby Yoshi, having not appeared enough yet. (The Ice Flower is also at the beginning of the level too).
Level 4-3 - Mushrooms
The 2nd level to be a Mushroom level, the first being World 1's secret level. It has Biddybud types again and introduces platforms that tilt to one side as Mario jumps on them. The Fire Flower and Bunny Suit are both recurring power-ups in the level.
Level 4-4 - Tower
A spooky tower with a big platform that is going up, like an elevator. Dry Bones and Spiked Balls drop down, and Enemy Boxes are featured. The level is quite hard because Mario and the Bros. have to dodge the Spiked Balls as they are rolling on the platform. At the top Pom Pom appears for the 2nd time, in a room filled with fire.
Level 4-5 - Sky
A level on a big bridge with Leaping Cheep-Cheeps, and again Lakitus. The Dash Baby Yoshi is the power-up helping Mario through the level, in addition to a Roulette Block. Also there are a set of Super Stars near the end so Mario is running fast.
Level 4-6 - Grass
A Grass level, with a pipe maze feel to it as there are pipes in lots of places. And where there are pipes, there are Pirahna Plants. Puppups and Hammer Bros. are also re-featured, and a ? Block gives out the Fire Flower.
Level 4-7 - Under-Ground
Yet another level taking place Under-Ground. The gimmick to this level is the newly introduced Monty Moles, along with their cousins, the Morty Moles. They are pretty much the only enemies in the level, exept a few Pirahna Plants which also appear.
Level 4-8 - Castle
The Castle of the boss from Super Mario Galaxy, the Lakitu King (or Giga Lakitu). This level has Thwomps in it, "Thwomping" as so to say. Spinies litter the King's battlefield, and Snake Blocks are featured across the lava.
Level 4-S - Forest
World 4 (Clear Skies)'s secret level takes place in a forest, introducing logs and refeaturing Ropes. The level also introduces the new replacement for Wigglers, the Jigglers, who jiggle as they walk living up to their names. Another and the final enemy introduced would be the completely new snake enemies known as "Vipersides", who attack Mario but only if he is looking at them. (The opposite of Boos prehaps).