Among the promotional material Mattel produces to bring attention to the Monster High dolls, the most prominent product is the Monster High cartoon series. Released as a mix of many webisodes of a few minutes long and a small amount of TV specials of around an hour, the cartoon is the primary medium through which new characters and accessories are brought to the audience's attention. The Flash-animated material was produced by W!LDBRAIN during 2010-2012 and is produced by Six Point Harness since 2013, though Top Drawn Animation has been continuously hired by both companies for supportive work after it took over from Caboom. Meanwhile, the CGI-animated material is produced by Nerd Corps Entertainment and DHX Media. Sound for the entire series is done by Salami Studios.
The cartoon is currently working through Volume 5. Mattel releases a new webisode weekly as long as an arc is running via the Monster High YouTube channel and the video portion of the Monster High website. The wait between arcs is not predictable at the moment. It also has loads of TV specials.
Between May 05th and July 30th of 2010, Mattel released 15 webisodes featuring the students, teachers and staff of Monster High. This was followed by a 3-month hiatus until October 29th, starting which another 12 webisodes were released until January 20, 2011. The webisodes of Volume 1 are 1:47 minutes long, good for a little less than 1:30 minutes worth of actual webisode. There is almost no continuity between the webisodes and all rely on the "gag-per-webisode" format. The Volume 1-associated TV special "New Ghoul @ School", which details Frankie Stein's first days at Monster High, functions as an alternative version of the webisodes' story.
Volume 2 was released between February 08th and November 17th of 2011. Its formula is drastically different from Volume 1's. Instead of only 1:47 minutes, Volume 2's webisodes take 3:32 minutes, almost twice as much. Moreso, the Volume 2 webisodes are heavy on continuity, featuring multiple storylines at once that span multiple webisodes. The TV special "Fright On!" was released during Volume 2's run and takes place between Volume 2 and Volume 3. Volume 2 also saw the release of a special webisode to promote the Kind Campaign, though it isn't marked as Volume 2 and has to take place after "Fright On!".
Preceded by three promotional webisode releases in October and November, the first of the regular Volume 3 webisodes was released on the Monster High channel and site on December 8, 2011. The end of Volume 3 is not any easier to define; the webisodes of the regular schedule stopped on December 10, 2013, but three final Volume 3 webisodes were released on the "Frights, Camera, Action!" DVD on March 25, 2014. All the Volume 3 webisodes are 2:31 minutes long, less than the length of Volume 2's webisodes, and mark a return to the "gag-per-webisode" format. There is still a sense of continuity a la Volume 2, but less so. Notably, Volume 3 introduced clip shows, which did help establish a sense of continuity. Nine TV specials belong to Volume 3, but none of them has a distinguishable position relative to the webisodes.
On November 21, five Volume 4 webisodes were uploaded on YouTube. Volume 4, like Volume 3, started while the previous volume had yet to reach its end.
On October 02 2014, a Volume 5 webisode was uploaded onto YouTube. Much like Volume 4, Volume 5 started before the previous volume had come to its end. Notable changes in Volume 5 are an increased running time, and a slight improvement in the animation itself, such as more varied facial expressions, and the exterior of Monster High's main building changing to look more like the school as seen in the movie specials.
On June 19 2015, a Volume 6 webisode was uploaded onto YouTube. Volume 6 seems to carry on the new changes made in Volume 5, including multiple-part webisodes.