Although every character has one or two, one scene stands out a lot: The fight scene between the two Syaorans in the Dream World might be one of the best action scenes Clamp ever made next to the final Subaru vs Seishiro. First of all, the area feels like a tribute the X/1999 dream scenes, the characters' movements are incredibly detailed, the two fighters employ lots of skills even if it lasts short, there is magic, drama and the ending comes with a big Tear Jerker. The Ovas gets some points for adding fitting background music. Not for nothing the Ovas kept promoting this scene.
Kurogane amputating his own arm without hesitation just to save Fai from the crumbling Celes
The fact that Clow Reed's magic was so powerful that his carelessly worded wish, without even intending it, broke down the multiverse.