Mojo

Mojo was first introduced in Just Dance 3, and has been featured in every game since then.

Just Dance 3
Mojo made its first appearance here, and you can unlock alternates depending on how many stars you get. Those can be Mashups, Alternates or new songs. The first thing you will unlock is Simon Says Mode (Jamaican Dance Mashup on XBOX 360). The last unlockable routine is Hungarian Dance No. 5 (I Don't Feel Like Dancin' Mashup on XBOX360).

Just Dance 4
Just Dance 4 pretty much worked in the same way as Just Dance 3, but there are more alternates. You will see an horizontal yellow bar in the right bottom corner that says "Mojo". Here, you can earn more Mojo by accomplishing Dance Quests. There are also alternates with items, and unlockable avatars. You need to fill the bar to win a surprise.

Just Dance 2014
Mojo started to work out differently here. Instead of Mojo, there are Mojocoins, that can be used to unlock alternate routines in the game. A Mashup usually costs 5 Mojocoins, an Extreme/On Stage usually costs 25 Mojocoins, and a special routine usually costs 50 Mojocoins. Another innovation is that you can unlock it any time. Past Just Dance  avatars cost 5 Mojocoins, Ubisoft game ones costed 50 Mojocoins, while the Unknown Disco Ball dancer cost 500 Mojocoins. There are also Sweat routines, Extremes, and other alternates. Also, when you get a DLC, you will get 1-2 exclusive avatars. Timber, Die Young, and Can't Hold Us, have two exclusive avatars.

Some songs can have a Mojocoins bonus, which gives 2 extra Mojocoins after playing it. The Mojocoins bonus occurs also when you are placed 1st in World Dancefloor or you beat the other team in a themed battle. Sometimes, there is an "Happy Hour" on World Dancefloor in which you can get 2 extra Mojocoins at every song.

Just Dance Wii U
Mojo worked similar to Just Dance 2014 with a few changes. They say "JD" instead of "M" and they can only be used to purchase avatars.

Just Dance 2015
Mojo pretty much worked the same as Just Dance 2014. However, alternate routines did not get unlocked with Mojo and instead by just playing the game. Mashups and Avatars can be bought for varying prices. Each Mashup costs 20 Mojocoins and the price for Avatars ranged from 5 to 50 Mojocoins.

Just Dance Now
Mojo was introduced in the October 22nd update and is obtained by leveling up in songs or by buying them with real money. Mojo can be used to purchase songs (excluding JD2016 and most new releases) enabling you to play the songs as many times as you want. Songs cost 150 mojocoins.

Just Dance 2016
In Just Dance 2016, the value of Mojo has dropped. One star would now bring in 100 Mojocoins instead of just one. Of course, the price for purchasable items has also risen accordingly. Each Mashup costs 1,000 Mojocoins, a normal alternate routine costs 2,000 Mojocoins, and an Extreme routine costs 10,000.

Yo-kai Watch Dance: Just Dance Special Edition
Similar to Just Dance Wii U mojo can be used to purchase avatars. Additionally they can be used to play the Gashapon mini game.

Trivia

 * Mojo seems to work out differently in all games.
 * Just Dance 2014 has the most unlockables.
 * Many different Mojo coins were in Just Dance 2014 and Just Dance 2015, making Beta appearances.
 * Where Have You Been has the most alternate routines: Mashup, Extreme, On-Stage, Battle and Party Master.
 * In Just Dance 2016 each star you obtain gains you 100 mojo coins instead of the ordinary 1 mojo coin per star obtained.
 * When I Grow Up is the only track with alternate routines (3) that are already unlocked from the start and does not need mojos to redeem with..
 * However, the alternate version of Barbra Streisand can also be unlocked without mojos, but must be unlocked with a D-Pad code.