For everybody who doesn't know about the game, here goes:
Little info has been released, but it has been confirmed that it will be a beat-'em-up style game where you play as Peach (duh). The bottom (touch) screen will be used for the main gameplay, i.e. moving Peach and attacking with the stylus. The top screen just shows Peach's face in various expressions (not very helpful other than to warn you that you've been hit, but it does show off the good sprite artwork). Judging from the screenshots, it appears as though you will use either Peach's classic frying pan weapon or a parasol or something. And while the DS is capable of much better graphics (they're about GBA quality), they are adequate.
Well, I hope this clears a few things up.
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"We get signal. Somebody set up us the bomb!" "What you say!" "All your base are belong to us!"
-Last Alert (PS1)