The dancer is a woman wearing a birthday/sweets-schemed costume. She is wearing a pink and sky blue top with sprinkles, a yellow and pink layered skirt, yellow polka-dot stockings with pink cupcake prints, and blue high heeled boots. She has long marigold hair tied in a ponytail braid and is wearing a floral wreath made of teddy bears and button flowers. She is wearing very heavy makeup consisting of blusher and eyeliner.
The background has a pastel scheme. There are also pictures of cake and confectionery appearing. The cake reads "Birthday". It is supposed to give the dance a birthday feel. You can see many macaroons around and you can also see them with candles lit.
There are 5 Gold Moves in the Classic routine: Gold Moves 1, 3, 4, and 5: Throw both of your arms up in the air while you lift up your right leg. Gold Move 2: Jump up with your legs fully up and hold both hands out as if you were confused.
Gold Moves 1, 3, 4, and 5
Gold Move 2
Gold Moves 1, 3, 4, and 5 in-game
Gold Move 2 in-game
There are 2 Gold Moves in the Mashup, both of which are the same:
Birthday is the tenth song by Katy Perry in the Just Dance series.
Just Dance 2015 came out in October, which is the same month as Katy Perry's birthday (Oct 25). The fact that this song by her is birthday themed will be featured makes it a huge coincidence. Not only this, but the game also came out just days before her birthday (either on October 21 or 23).
Unlike other dancers with makeup that is hardly visible in game, this dancer's makeup is clearly visible.
The dancer lip syncs "Happy Birthday" every time the line is sung.
The Mashup for this song only features other songs by Katy Perry. The dancers for all the songs by Katy Perry, except Roar, are featured in the Mashup.
This is the first time a dancer from any non-Solo routine (in this case, a Trio) is used as a Solo dancer (the Dark Horse lead dancer).
Also, this is the only Just Dance 2015 Mashup that features at least one coach from every game of the main series.
When unlocking the avatar for this song after playing it, the lipstick is absent. However, when you look at it in the Avatar Shop, the lipstick appears.
This also happens with Cool For The Summer’s avatar on the seventh generation console versions of Just Dance 2016, as the collar is purple when unlocking it, while in the avatar shop, the avatar has a golden collar with spikes.
The first time Hot N Cold appears in the Mashup, the transition is not smooth like in other Mashups, but rather, it seems very sudden much like the transitions in Maneater’s Mashup.
There was a VIP on the World Dance Floor named Aurélie during most of November 2014. Players could dance with her while this song was played on the World Dance Floor. As of January 2016, it is back.
In the preview video, the arrows for the pictograms were dark pink, despite the glove being red.
This song won in the Favorite Choreo category on the second Just Dance Awards. 
In some beta gameplay snapshots, the coach appears to have a blue glow instead of a solid border like in the final version. In another, the coach's outline is orange instead of blue.