Narcotic accidently had Princess Candence infected with the Engoritis virus, a common AUU non-fatal disease that causes inflammation of the skin and causing a fat appearance. While the forgiving Celestia sent Cadance to an Alternate UUniversal hospital to deal with the sickness, she went out to get a substitute teacher for the Reforming Monastery. Meanwhile, The Dark Order has used the Morphogen 5000 to combine a suit of armor with a gazelle child. But what they didn't know was that there was a third combination: the child's mantis friend was attempting to rescue her, and ended up getting blended. The result was the Substitutioner, a creature with a rock-hard hide, mantis-like characteristics, and a beautiful gazelle body. This creature had not just been corrupted, but the gazelle's body aged 10 years. Or-Gan knew that this was a perfect choice for gaining extra recruits. He sent Substitutioner in as the replacement, under the name 'Joan Crosser' after the gazelle's first name and the mantis' last name. But unbeknownst to them all, Cadance has been able to recover quickly from the disease, and begins spying on the Substitutioner to see what she's up to. But Twilight is able to discover what the Substitutioner is up to first, and warns Celestia. While the Shell Lodgers are on their way, Cadance decides to hold off the Substitutioner until they arrive. But it seems the Substitutioner was onto Cadance the whole time, and locks her up in the detention center. Now, Cadance must find a way to escape before Substitutioner begins her plans of corrupting the many residents of her Monastery. But outside of the armor, Substitutioner's biggest defence is that it was once the innosent child and her friend, so just flat out killing her is out of the question. But luckly, there's more then one way to stop a mutant, and Xenon already offered such a suggestion by giving them a speical demutantion gun capable to reseverse even the most powerful of mutantions!