There are only a few characters that appear within the parks during regular hours that offer special Christmas costuming. Phineas and Ferb and Goofy after dark dress up at Hollywood Studios and Duffy appeared as Santa in Epcot, but the Animal Kingdom is a smorgasbord of Disney characters in special holiday outfits. You can find Mickey, Minnie, Donald, Chip n Dale, Goofy, Pluto, Winnie the Pooh, Eeyore and Tigger in great festive attire. My daughter and I spent a day in the Animal Kingdom recently and met each of these characters.
Goofy and Pluto in Dinoland