[1] Following colorful creatures known as Mixels, the series depicts their exploits involving their ability to combine with one another in order to solve problems or fight against their enemy: the Nixels.

Although previous Lego series, such as Lego Ninjago and Lego Legends of Chima, use CGI animation, Mixels made use of Toon Boom Harmony software, animated at Atomic Cartoons, Inc., before later being animated traditionally at Digital eMation, Inc., Big Star Entertainment, Inc., and Saerom Animation, Inc. A mobile app was released for the series on March 4, 2014, named Calling All Mixels, and even earlier two websites, one on the LEGO website and another owned by Cartoon Network, were launched where fans can learn about the Mixels.

A group of Mixels set out on a quest for the mythical Mixamajig without knowing that it is part of King Nixel's plot.

Booger must stop King Nixel from replacing Cubits with "I-Cubits" and taking over Mixopolis.

Some design changes include Shuff and Seismo's names being swapped with each other, Shuff having a looser crystal on his head that would have looked more like hair, Vulk's ears being red instead of black, the Nixels coming in various shapes, and Balk originally being shorter and squatter with thinner tentacles and smaller pupils.

Anderson also highlighted the importance in the characters' faces in capturing a unique personality and explained, "The eyes and mouths are a huge part of the personality of the Mixel, changing the eyebrows for example can drastically change the expressions from sad to happy, or even angry!

[7][8] On Lego's promotional website for the series, a Mixels building set released in 2015 was described as a "back-of-the-bus window-licker", which is considered a derogatory term in the United Kingdom.

Following negative reception from British media outlets, an apology statement was issued by Lego, and the term was removed from the product's online description.