You know? I think this picture could actually have a minor spoiler about the next special episode "Phineas and Ferb: Mission Marvel".
According to an interview to Dan Povenmire and Jeff Marsh, Candace is a fan of Thor; and what a coincidence, she appears dressed like a viking warrior here. By promotional pictures of the special, we have already saw Phineas and Ferb as the Beak again; which emulates Iron Man. And we have seen Baljeet turned into something that it looks like a "mini-Hulk" too. Do you think Candace will use this viking outfit in the special too, emulating Thor? With this, I just wonder who could emulate Spider-Man.