Signature

Despite a growing and changing assortment of dolls and doll lines, throughout the years since Monster High ' s take-off, there is one stable, ongoing line. This line, recognizeable by assortment number N2851, is without a name, on account of it containg the 'default' dolls and thus not needing a specifier. This "main" series of dolls primarily represents the characters as they commonly appear in fiction, but the number of main dolls in alternative outfits is steadily growing. They are released in sets of 7 à 8 dolls that in marketing, release dates, and diary content share significant common ground. Most of these sets are nameless too, but fans have made up names themselves to distinguish between the sets.

Overview
It is currently uncertain if V4 has ended or is still ongoing. The next main doll on the release schedule is Headless Headmistress Bloodgood, but as the current situation of the main dolls isn't clear, so isn't which set she belongs to, if any. Invisi Billy has also been semi-announced as part of the main line, but when he is to be released is unknown.

C.A. Cupid, listed as the sole doll of V5, was released as the sole new main doll among a set of five re-released dolls. The other four—School's Out Clawdeen Wolf, School's Out Spectra Vondergeist, School's Out Frankie Stein, and Basic Draculaura—were main line re-releases and the whole set was explicitly marketed alongside the regular main releases. This setup was repeated the next year, when in Late January, 2013 Basic Clawdeen Wolf, Draculaura, and Frankie Stein were re-released as the Original Favorites subline in Europe, while the re-release subline hit the USAmerican market in May.

History
Between the first set, the Basic subline, and the second set, the School's Out subline, five characters are shared. To be able to distinguish between them, the fandom thought up the term School's Out for the second subseries, while reserving the term Basic for the first subline and the non-repeated characters of School's Out. However, this practice was and is not consistent, which has led the wiki to define Basic and School's Out solely as identifiers of the respective waves regardless whether a character is repeated or not. The same principle goes for each subsequent wave.

The Basic Ghoulia Yelps and Holt Hyde dolls technically also belong to the School's Out subseries, on account that they have been re-released in School's Out packaging and were marketed as School's Out dolls in June 2011. This was probably done because they had not been out for that long when School's Out hit the shelves. However, since both dolls are the same and come with the same accessories, the wiki only lists them as Basic for management purposes.

Campus Stroll introduced store exclusives to the main series with the Early 2012 Meowlody & Purrsephone and Clawdeen & Howleen Wolf 2-packs, though it took a year before another main line store exclusive was released, that time Headless Headmistress Bloodgood.

The Late 2011 release of C.A. Cupid in the Sweet 1600 series was the first time a default doll was not released in a main subline. She was later released without any changes but with a diary to the main line. This was followed up with the SDCCI releases of Scarah Screams and Hoodude Voodoo, but they obviously were never added to the main line.

The next default dolls not to be released in a main subline were Late 2012's Jinafire Long, Skelita Calaveras, and Early 2013's Catrine DeMew, which were all part of Scaris: City of Frights. Unlike C.A. Cupid, each of them did come with a booklet, which in the first two's cases functioned as a diary.

Along with Scaris: City of Frights, Late 2012 saw the introduction of Picture Day, the first named and themed subline of the main series. It introduced no new characters, whereas the unnamed main subline immediately preceding it marked itself by containing no repeat characters. Therefore, Picture Day appears to signify a split in the main line, with new characters getting releases in the non-themed sublines, and repeat characters getting releases in lightly themed side-sublines.