Super Mario Land 2: 6 Golden Coins
Mario in the Tree Zone.
PROLOGUE:
Mario was in Sarasa Land when battling an intergalactic fiend called Tatanga. After Mario foiled Tatanga's plans of marrying Princess Daisy, Mario returned to his private island, Mario Land. When he arrived, he noticed that Wario, his evil counterpart, who was jealous of him since they were kids, took over his castle  and the Six Golden Coins of Mario Land are missing (not to mention Wario's minions are here also). It's time to save Mario Land!!
EASY MODE CODE:
At the Game Select screen, press Select and enter your game file. Now the game will be easier than it needs to be 'cause the game is easy even if you're not playing Easy Mode!!
BOSS GUIDE:

Bird- Jump on its head three times. Dodge its Dive Bombs.

Witch- Will appear on either the left side or the right side. Jump on her head three times.

3 Little Pigs- Straw house pig rolls. Stickhouse pig jumps. Brickhouse pig BOUNCES! Jump on each of them three times.

Octopus- Jump on his head 3 times. Dodge its attacks.

Tatanga- Duck under his fireballs and when he swoops down, jump on him. Three hits will do it.

Giant Rat- He'll run down from a pipe. Jump on it when you get the chance. Three jumps will kill it.

Wario- Phase 1. Jump on his head 3 times. Watch for falling chandeliers. Phase 2. Bunny Wario. Dodge his stomps and jump on his head three tmes. Phase 3. Fiery Wario. Jump over his fireballs and jump on his head 3 times. Phase 4. THE END.

Note that all bosses except for Wario can be defeated with fireballs. It helps to have Bunny Power when fighting Wario Phase 3.
There are secret entrances to secret levels in Mario Land 2. There are 2 in Pumpkin Zone, 1 in Macro Zone, 1 in Tree Zone, 1 in Turtle Zone and I think there's one in Mario Zone. Find them and beat them to see a change on the maps of the different zones.
On a level you've already beaten, press Start then Select to exit the level instantly. This also works in Super Mario World and Yoshi's Island.
                         PLAYABLE DEMOS
At the title screen, press any of the following to play demos.
Mushroom Zone- Press Up and A.
Space Zone Entrance- Hold Up and A and press  Select.
Macro Zone- Hold Up, A and B then press Select.
Turtle Zone- Hold Up and A then press Select.

Note that these control demo codes only work on the version of Mario Land 2 that
DOESN'T say Players Choice Million Seller.
BONUS TIP:
In the original Super Mario Land, if you beat the game twice in a row, after all of that ending crap, on the title screen, press A. The more you press A, the farther in the game you'll start at.
To kill Skeleton Bees, just do a Spin Jump on top of them!
Touchdown!
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