The forth World of New Super Mario Bros. 3 (Silver-zoroark's version). World 4 takes place in mines, and it is a bit mountainous too.
Mine Carts and Monty Moles are introduced. The Monty Moles throw Bob-Ombs when coming out of Pipes. The level takes place in a cave.
This level takes place outside the cave, in the rocky mountainous terrains. There are Bullet Bills and Chain Chomps, and a Fire Bro. at the end of the level.
Boulder Spikes are introduced, and Mario is given the Boomerang Flower. Also there are some Bob-Ombs in certain places.
A "mechanical" Tower, with Conveyer Belts, Bullet Bills, Chain Chomps, and Bob-Ombs. Also there are some Buzzy Beetles.
Level 4-Ghost House
In this Ghost House the Boohemoth is back, and the level has Splunkins and a Beanstalk. It also features staircases, not seen sence World 1-Peach's Castle.
Half outside, half in a cave. There are Lakitus and Monty Moles so the level can get complicated. Also the level introduces Elite Moles, which are a sort of harder Monty Mole that takes two hits.
The first level in the sky for a while. It has moving mushrooms, and is one of the first sidescrolling levels, unfortunately. It also introduces Banzai Bills, who appear at the end of the level.
There are Monty Moles, Bob-Ombs, and lots of stuff. Also Mecha-Koopas are exclusive to this Castle. The boss has been yet to be announced by the creator.
Easy - 4 Monty Moles
Medium - 2 Monty Moles and 2 Elite Moles
Hard - 4 Elite Moles