Wings

Cross doesn't want them to know, he doesn't want Nightmare to find out or anyone to find out between Killer's Raven wings with hidden feathers as sharp as blades, Dust's Falcon wings that are the fastest in the sky and Horror's Condor wings large and imposing forcing enemies from the sky his wings were pathetic they were small and fuzzy with downy feathers he couldn't even fly with them yet though they wouldn't be fuzzy next year, next year he'd shed all his downy feathers for flight feathers he just had to hide the fact he wasn't an adult yet.

He could do that, how hard could it be?

Or Cross is trying to hide the fact he's 17 when everyone thinks he's out of stripes because he's scared that Nightmare and the others will send him back in his abandoned world.