Mini Mario Card

Mini-Mario Cards are cards with a picture of Mini-Mario and a letter on the back in Mario vs. Donkey Kong 2: March of the Minis. There are 9 cards in each world, and getting all of them will unlock a Mini-game.

All the cards together spell out: "MINIMARIO". The level number of a floor corresponds to the letter as it appears in "MINIMARIO" (i.e. Level 2-5 has a M card).