Queen Mab

Queen Mab is based on a fictitious character in Romeo and Juliet, and was scheduled to appear as a side-character in Christmassy Yet Again! and the cancelled Society's Brandy Balls. She eventually makes her grand introduction in One of our sandwiches is missing! as the primary antagonist, haunting the copy of Sonic 2 that Matt and Comic Fan 13 have been reviewing.

Why her exactly?
The origins of Mab's inclusion in TME spawn from multiple In-Jokes created by Matt and Cosmo whilst studying Romeo and Juliet - similar situations occur when references are made to other texts the two have been studying (such as Frankenstein, A Streetcar Named Desire and Philadelphia, Here I Come! respectively). Since most of the jokes were made by Cosmo, he was automatically cast as Mab for "One of our sandwiches is missing!".