A mean substitute creature makes Deuce take off his sunglasses in class. The result? A really rockin' day at Monster High!
Heath Burns and another student consider the benefits they can reap from the fact that today's Trigular Calcometry 101 will be handled by a substitute teacher. At the same time, Lagoona, Clawdeen, Draculaura, Frankie, and a noncommitted Cleo wonder what happened to Headless Headmistress Bloodgood, who is the regular teacher of that class. They discuss the rumors they've heard, but shut up when Ghoulia arrives and contributes a particularly gross rumor.
The substitute teacher demands silence so he can begin class. He introduces himself as Lou Zarr and writes his name on the chalkboard, prompting Heath to loudly pronounce it as "loser" and the class to laugh. Mildly exasperated, Zarr corrects him and orders the students to open their books. He adds that since he doesn't know how much of its content has already been covered in previous lessons, they're going to do the whole book. At that moment, Deuce comes walking in like he's not late at all, but Zarr isn't willing to let it slip. Deuce, surprised that Bloodgood isn't teaching, asks the substitute teacher's name and ends up pronouncing it "loser" too. The whole class laughs again. Deeply exasperated, Zarr demands that Deuce takes off his sunglasses in his class. Deuce only answers that Zarr wouldn't want him to do that, but Zarr says he insists. As such, Deuce obeys, no little amused and only after his classmates have hidden themselves behind their books.
Lou Zarr is petrified by Deuce's gorgon glare. Without teacher, Deuce announces the class dismissed. The rest of the class happily pours into the hallway, though not after leaving paint, a lampshade, and a banner reading "dork award" on Zarr's petrified form. Deuce stays a little longer to semi-apologize and tell Zarr that the effects of his glare wear off in a few hours... usually.
- A "creature" is the Monster High version of a "teacher".
- Lou Zarr calls the class "little freaks", somewhat implying that humans discriminate against monsters. This was confirmed in "Escape From Skull Shores" and "Ghouls Rule". Similarly, the class appears to have little willingness to deal with Zarr, which matches the theme that would be introduced with Jackson Jekyll from "Fear Pressure" onwards.
- The TV special "New Ghoul @ School" incorporates the story of "Substitute Creature" into itself, having Lou Zarr lose control of the class because he is boring rather than agitated, and thus represents an alternative sub-continuity.
- Heath Burns and Lou Zarr make their cartoon debuts, though it won't be until "New Ghoul @ School" that Heath is named. Headless Headmistress Bloodgood is mentioned but won't make an actual appearance until "Totally Busted".
- "Substitute Creature" is the first time a human is seen in both the cartoon series and Monster High as a whole, establishing that humans do exist in the franchise's universe.
- Lou Zarr is the first teacher, Monster High staff member, and adult featured in the cartoon series.
- The description of the webisode states that Mr. Zarr is "mean". This is a rather biased description, considering several other teachers would turn out to be much meaner than he without provocation and still receive much more respect from the students. If anything, it's the students that are mean in "Substitute Creature".
- This webisode features the first time that Ghoulia says something in Zombie that the other girls respond to in disgust. This is later done again in "Frightday the 13th", including Frankie's exact response of "Oh, that's ghastly!".
- This is one of only three appearances of Lou Zarr. The other times are in "New Ghoul @ School" and the Monster High website game Creepateria Food Fright. Though called a substitute teacher in "Substitute Creature", he appears to be a regular teacher in his other appearances.
- Most of Lou Zarr's animation was also used in "New Ghoul @ School".
- Deuce's biggest pet peeve in the Monster High website game Registration is "substitute creatures". That is a reference to this webisode, as the biggest pet peeve on his profile is just "people who annoy me".