Penny’s always excited about the possibility of other dragons being around while Percy is a bit scared of other dragons due to being dropped off at the Everfree Palace at a young age when Penny was just a hatchling, hence his nervous look.
Percy and Penny are from back when Tia and Luna were kids so this might not be timewise accurate but I’m sure they’d all get along well. :3
MLPFIM © Hasbro
Percy and Penny © Me