If I used Pounce on Colossal Boy, could he perplex his damage value down from 3 to 2 and then use Pounce?

Thanks

No. From the Danger Room rule book (page 46):

In order for a character to use an assigned feat, any prerequisites for the feat must be printed on the character’s base or visible on its combat dial through the stat slot. If using a feat requires giving the character an action, then the prerequisites must be present on the combat dial at the time the player gives the character the action. Combat values cannot be modified to meet the prerequisites to use a feat. A character that already meets the prerequisites to use a feat may have its combat values modified as long as the modified combat values still meet the prerequisites to use the feat. A feat assigned to a character is in effect during an action unless the player who controls the character indicates at the beginning of the action that the feat is not being used. The feat resumes its effect immediately following the completion of an action during which it is not used.

edit: Yeah, what Normalview said.