Woah! There's a thread on this!? This is one of my favorite DS games! When I first got the game, I made a microgame where Mario has a Boo on either side of him, and you have to look in different directions to stop one Boo, and keep them away from you for the time limit, using copies of the Super Mario World sprites. Afterwards I got the Wiiware channel, and I found a game that was almost the exact same! The only real difference is that it was Super Mario Bros 3 sprites. Either way, it was funny!
Try experimenting with travel actions, and combining them, especially target and roam, then think of what kind of game can work well with that combination of travel actions. Remember to experiment with the speed as well.
For example, I made an archery game, where you tap once to choose the power level, and tap again to choose the angle. The power level is a three section bar, and the angle is a cursor that reflects in an area. At the second tap, the arrow's first action is to target the cursor, and the second is to bounce, giving it the effect of gravity. It will target the cursor at a different speed depending on the power level after the second tap.