Action Replay: Mario Kart - tiny - Nintendo DS

Action Replay: Mario Kart - HUGE - Nintendo DS

Action Replay: Mario Kart - Drive on Test Circle - Nintendo DS

Action Replay: Mario Kart - Fly - Nintendo DS

Action Replay: Mario Kart - Invisible - Nintendo DS

Action Replay: Mario Kart - Freeze Time - Nintendo DS

Action Replay: Mario Kart - Untouchable - Nintendo DS

This cheat will complete all the race missions with 3 stars including the secret one in Mario Kart. Here’s the code:
023d00c4 0f0f0f0f
023d00c8 0f0f0f0f
023d00cc 0f0f0f0f
023d00d0 0f0f0f0f
023d00d4 0f0f0f0f
023d00d8 0f0f0f0f
023d00dc 0f0f0f0f
023d00e0 0f0f0f0f
023d00e4 0f0f0f0f
023d00e8 0f0f0f0f
023d00ec 0f0f0f0f
023d00f0 0f0f0f0f
023d00f4 0f0f0f0f
023d00f8 0f0f0f0f
023d00fc 0f0f0f0f
123d0100 00000f0f
223d0102 0000000f
You can buy an Action replay here. They are definitely worth it:

Action Replay: Mario Kart - Mushroom Speed - Nintendo DS

Action Replay: New Super Mario Bros - Tiny Mario - Nintendo DS