The Whac-A-Mole game from Episode 40, the Dream Card episode. Sakura was struggling to hit all the moles coming from all around her, so Meilin decided to grab a hammer and help her out. With each other's backs covered, they had the time of their lives smashing up moles. Especially awesome is that Meilin used to hate Sakura with a passion and constantly distrust her when they first met, but at that moment, they were playing together like they've been best friends forever.
Against the Twin Card, Syaoran and Meilin's perfectly synchronized attack was the greatest display of Badass Normal in the whole series.
The second greatest being Meiling vs the Fight Card.
Also, how Sakura caught The Jump. Specially because at some point the girl (who mind you, was still a Na´ve Newcomer and basically realising how the deal worked) summons The Fly while taking a huge fall and being upside down. A little mistake and she would've died, but she managed to get this perfectly done.