Mario vs. Donkey Kong 2: March of the Minis Cheats - DS

Unlock Construction Kits
Jungle Hijinks construction kit - Beat Donkey Kong at Jungle Hijinks.
Lava Dome construction kit - Beat Donkey Kong at Lava Dome.
Magnet Mania construction kit - Beat Donkey Kong at Magnet Mania.
Mushroom Mayhem construction kit - Beat Donkey Kong at Mushroom Mayhem.
Pipe Works construction kit - Beat Donkey Kong at Pipe Works.
Spooky Attic construction kit - Beat Donkey Kong at Spooky Attic.
Toadstool Castle construction kit - Beat Donkey Kong at Toadstool Castle.
Tropical Island construction kit - Beat Donkey Kong at Tropical Island.

Mini Game: Shy Guy Smash
Collect all of the Cards (one in each level to spell out MINIMARIO) to unlock the Mini Game for that world. The Minigame is always Shy Guy Smash, but of varying degrees of difficulty and different Pipe layouts. Beating the Minigames will send you on the way to get the Special Construction Kits:

Special Kit 1 (Mini-Toad) - Beat Three of the Minigames
Special Kit 2 (Mini-Peach) - Beat Six of the Minigames
Special Kit 3 (Mini-DK) - Beat Nine of the Mini-Games

Unlock title screen characters
You can unlock different minis to stroll across the title screen by getting various medals in the game (purely cosmetic). It also changes the music at the title screen to a retro theme:

Donkey Kong Minis - Get Golds on all 80 levels
Princess Minis - Get Silvers on all 80 levels
Toad Minis - Get Bronzes on all 80 levels

Unlock Pictures
Picture 1&2 - Beat DK in floor 1
Picture 11&12 - Beat DK in floor 6
Picture 13&14 - Beat DK in floor 7
Picture 15&16 - Beat DK in floor 8
Picture 17 - Beat DK in Roof
Picture 18 - Beat Hidden Boss 1(B1) in basement
Picture 3&4 - Beat DK in floor 2
Picture 5&6 - Beat DK in floor 3
Picture 7&8 - Beat DK in floor 4
Picture 9&10 - Beat DK in floor 5