While Mario is away in Sarasaland, Wario arrives at Mario's castle and takes over. Wario put's an evil spell over Mario Land, making the inhabitants think that Wario is their leader. He then seals the door of Mario's castle and takes the six golden coins that hold it shut and scatters them across the land. The objective of the game is to get all six coins and enter the castle to confront Wario.
This is the first game in Nintendo history to feature Wario, that lout.
The game generally plays like any Mario platformer would, with some interesting exceptions. Mario proceeds from left to right in his search for the exit to the next stage. Once he reaches this exit, he will discover a bell hanging above it. To reach this bell usually takes some extra effort, but if he manages to ring it he will be taken to a mini-game where he can earn powerups and extra lives, assuming he doesn't accidentally walk off the screen before he's awarded the prize.
New to the Mario series, and never seen again afterward, is Bunny Mario. After eating a Super Carrot, Mario transforms into Bunny Mario and can glide by twitching his ears up and down. Bunny Mario cannot fly technically, he can only slow his descent as Bunny Mario, similar to the glide effect given by the racoon and tanooki suits in other SMB games. Why this change was never later used is unknown, but at least you get to ponder how rabbit ears could possibly help Mario take to the skies.
Mario selects worlds from a map, taking each world on in any order. The map has six different zones, each with 3-4 levels in them. There's the Tree Zone, Space Zone, Macro Zone, Pumpkin Zone, Mario Zone and Turtle Zone.
In an interesting change, instead of a 100 coin counter, the coin counter goes up to 999, and doesn't roll over to zero or give you extra lives. The coins are used in a special zone where you play a game of chance to try to win awards, including fire flowers, bunny ears, extra lives, recovered coins, and a booby prize in the form of a witch, who gives you nothing. it is also possible to accidentally pick up more witches in certain areas, and these witches will be added to the minigame board, increasing the chance that you'll get nothing for the coins you risked.
There is another counter, which goes up to 99, but this is a KILL counter, and when THAT reaches 100 kills, you are awarded with an invincibility star no matter where you are in the stage. This can potentially lead to more extra lives if you can kill enough enemies in combination before the invincibility runs out, and because it can occur anywhere on the stage, it can suddenly be very helpful in getting past certain areas (or it can be all but useless, depending on your timing).
Another interesting fact is that this game is one of the few Mario games to feature a multi-stage boss that takes a total of more than 3 hits. In a sense, it's a combination of 3 successive bosses that total 9 hits, creating a bit of tension when you realize that you have a ways to go before you win.
Turtle Zone - Consists of three water themed levels. When Mario first enters the zone he gets swallowed by a giant turtle. The boss at the end of the zone is an octopus.
Mario Zone - The zone looks like a giant toy Mario. Its four levels have a toy theme to them. The bosses at the end of the zone are The Three Little Pigs.
Pumpkin Zone - All four of the levels feature a scary theme. The zone looks like a giant pumpkin. The boss at the end of the zone is a witch.
Space Zone - This zone consists of three space themed levels. To get to this zone you must first beat a level that looks like a giant hippo on the map screen. In these levels, gravity is much lighter and Mario's jumps take him much farther. He also wears a space suit in all of the levels. The boss at the end of the zone is the alien Tatanga, the final boss from the first Mario Land game.
Macro Zone - For this zone Mario shrinks to a small size while he enters a normal house. It consists of four levels. The boss at the end of the zone is a giant rat.
Tree Zone - This zone consists of four levels set in a gigantic tree. All the levels are tree based on different parts of the tree. The boss at the end of the zone is a crow.
Final Zone - This zone takes place inside Mario's Castle which has been warped to suit Wario's needs. The boss at the end of the zone is Wario himself who must be defeated three times. The first time he attacks he runs back and forth across the screen and slams into the ground dropping a light from the ceiling to try and hit you. After three hits, he escapes off screen. He then attacks as Bunny Wario. In this form, he leaps to the top of the screen and flys back and forth while slowly descending before slamming into the ground dropping the light and freezing you in place for a second or two. After another three hits he escapes one final time. He then transforms into Fire Wario. He attacks by running back and forth and shooting fireballs at you. After the final three hits he turns into Baby Wario and is defeated.
It was announced for a Q4 2011 release on the 3DS Virtual Console.