Complete Compendium of Escape Rituals is a book that the Mad Dogs seek to retrieve from the Mystic Library in order to save Mayhem who had become trapped in April O'Neil bathroom mirror.
After discerning the book's location from the library's catalog, Donatello uses a rhyming song as a mnemonic to find the book, but gets carried away by the Hush-Bats after singing it too loudly. Raphael uses the mnemonic to retrieve the book, destroying a large portion of the library in the process.
Upon returning to April's apartment, the Turtles use the Compendium to free Mayhem from the mirror, only for Mayhem to teleport back into the mirror seconds later to avoid a bath.