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Snow White: Signature dress with red cape
Cinderella: Peasant dress
Aurora: Peasant dress
Ariel: Blue dress (as seen in Kiss the Girl)
Belle: Pink dress with cape
Jasmine: Purple celebration outfit
Pocahontas: Native American dress with necklace
Mulan: Blue dress (from the end of the film)
Tiana: Green celebration dress
Rapunzel: Pink dress
Merida: Blue-green dress with cape
Anna: Grey dress
Elsa: Coronation outfit

Sequels included? If not, my second option will be in parenthesis. (:

Snow: Blue and Red Dress with Cape
Cinderella: Wedding Dress
Aurora: Peasant Dress
Ariel: First White Dress from TLM 2 (or Blue Dress)
Belle: Dark Red Dress from BatB Christmas (or Yellow Dress)
Jasmine: Purple Celebration Outfit
Pocahontas: Ball Gown from Pocahontas 2 ( or Short Dress with Necklace)
Mulan: Blue Dress
Tiana: Blue Waitress Outfit
Rapunzel: Pink Celebration Dress
Merida: Dark Green Dress
Anna: Light Green Dress - the one at the end of the movie
Elsa: Coronation Dress with Cape

Oh, sequels count.

Snow: Princess dress with cape
Cinderella: Silver Ball Gown
Aurora: Peasant dress
Ariel: Blue dress
Belle: Ball Gown
Jasmine: Red Outfit
Pocahontas: Her short dress
Mulan: Pink Dress
Tiana: Almost There Dress
Rapunzel: Pink Dress
Merida: Dark blue Dress
Anna: The blue dress with Pink cape
Elsa: Coronation dress with cape

Snow: Princess dress with cape
Cinderella: Silver Ball Gown
Aurora: Pink Dress
Ariel: Pink Dinner Gown
Belle: Gold/Yellow Ball Gown
Jasmine: Purple Dress
Pocahontas: Ball Gown from the sequel
Mulan: Pink Dress
Tiana: Green Ball Gown
Rapunzel: Purple Dress
Merida: Light blue dress
Anna: The green coronation dress
Elsa: Light blue dress

Snow White: Princess Dress
Cinderella: Wedding Dress
Aurora: Peasant Dress
Ariel: Sparkly Dress
Belle: Christmas Dress
Jasmine: Purple Dress
Pocahontas: Forest Outfit With Necklace
Mulan: Blue Dress
Tiana: White Dream Dress
Rapunzel: Wedding Dress
Merida: Dark Blue Dress
Anna: Coronation Dress
Elsa: Blue Dress

Snow White: Iconic dress with cape
Cinderella: Silver ballgown
Aurora: Peasant dress with shawl
Ariel: Wedding dress
Belle: Pink dress with winter cloak
Jasmine: Purple celebration outfit
Pocahontas: Sequel ballgown
Mulan: Purple sequel outfit
Tiana: Borrowed sparkly blue dress
Rapunzel: Purple dress
Merida: Light blue dress with wimple
Anna: Coronation oufit with green cape
Elsa: Snow Queen dress with ice cape

Snow White: Signature dress with red cape
Cinderella: Wedding dress
Aurora: Peasant dress
Ariel: Sparkly dress
Belle: Ball gown
Jasmine: The dress at the end
Pocahontas: Forest outfit
Mulan: Green dress
Tiana: Borrowed sparkly blue dress
Rapunzel: Wedding dress
Merida: Dark dress with cape
Anna: Winter dress
Elsa: Blue dress

Snow White: Signature dress with the cape
Cinderella: The Pink Dress
Aurora: Blue dress with hood
Ariel: Blue town dress
Belle: Christmas dress
Jasmine: Red outfit
Pocahontas: Forest outfit with necklace
Mulan: Father's armor
Tiana: Green bayou wedding dress
Rapunzel: Child dress
Merida: Dark dress with cape
Anna: Green dress
Elsa: Coronation dress with cape

Snow White: Signature Dress With Red Cape
Cinderella: Wedding Dress (Third Movie)
Aurora: Pink Ballgown
Ariel: Pink Dress
Belle: Pink Dress With Cape
Jasmine: Purple Outfit (End of first movie)
Pocahontas: Ballgown
Mulan: Matchmaker Outfit
Tiana: Second Wedding Dress
Rapunzel: Pink Dress
Merida: Light Blue Dress
Anna: Green Coronation Dress
Elsa: Snow Queen Dress

Snow White: Servant dress (she looks cute in it)
Cinderella: Ball dress (simple but beautiful...but please in white/silver, not in blue)
Aurora: Peasant dress (though I like the blue dress with blue cape just as much)
Ariel: Silver dress
Bell: Pink dress with cape
Jasmine: Difficult...I guess her regular outfit
Pocahontas: Her usual outfit
Mulan: The blue dress she wears at the end...it's mostly her. Alternative the green one.
Tiana: The white dream/Almost there dress
Rapunzel: Her wedding dress
Merida: The green dress with cape

Snow White: Princess Dress with Cape
Cinderella: Silver Ball Gown
Aurora: Blue Ball Gown
Ariel: Sparkly Purple Dress
Belle: Pink Dress With Hood
Jasmine: Purple Celebration Outfit
Pocahontas: Forest Outfit
Mulan: Blue Dress
Tiana: White Dream Dress
Rapunzel: Wedding Dress
Merida: Dark Green Dress
Anna: Green Coronation Dress
Elsa: Ice Dress

Snow White: Princess dress with cape
Cinderella: Silver ball gown
Aurora: Peasant dress
Ariel: Sparkly purple dress
Belle: Yellow ball gown
Jasmine: Red outfit
Pocahontas: Forest outfit with necklace
Mulan: Blue dress
Tiana: Green ball gown
Rapunzel: Pink dress
Merida: Black dress
Anna: Coronation dress
Elsa: Ice dress

Snow White: Servant dress
Cinderella: Servant dress (you know what, I like them, okay?)
Aurora: Blue gown with cape
Ariel: Blue town dress
Belle: Green dress with cape
Jasmine: Purple engagement outfit
Pocahontas: Oooh, tough, I like pretty much all her outfits in both movies- I guess the winter dress from the sequel?
Mulan: Armor with helmet
Tiana: Almost There dress
Rapunzel: ...Normal dress?
Merida: Ending dress
Anna: Coronation dress
Elsa: Ice dress

Snow White: Peasant dress. (Yes, even with the terrible hem.)
Cinderella: Silver ball gown.
Aurora: Peasant dress.
Ariel: Blue town dress.
Belle: Green dress with cape.
Jasmine: Aladdin ending outfit.
Pocahontas: The only one she wears in the movie. xD
Mulan: Green dress (from the beginning).
Tiana: Yellow waitress dress with green coat and hat.
Rapunzel: Pink dress from the ending.
Merida: Everyday dark navy dress.
Anna: Blue winter dress with pink cape.
Elsa: Coronation dress with purple cape.

Snow White: Servant Dress.
Cinderella: Pink Dress.
Aurora: Pink Princess Dress.
Ariel: Sparkly Dress.
Belle: Pink Outfit.
Jasmine: Red Outfit.
Pocahontas: Ballgown, if the sequel counts - if not, her only dress in the movie.
Mulan: Purple Dress, if the sequel counts - if not, her Matchmaker Visit Dress form the original movie.
Tiana: Orange Outfit.
Rapunzel: Purple Dress.
Merida: Blue Dress.
Anna: Black Dress.
Elsa: Ice Dress.