Following Agatha's adventures in the Paris underworld, it is revealed ✣ that the Immortal Library has in its possession a humanoid clank called the Muse of Vengeance. It is evidently not one of the "official" Muses created by uber-Spark Van Rijn for the original Storm King, though being the founder of the Library, the probability that Van Rijn also constructed it is high.
As indicated by its name, the currently dormant Muse is a large and imposing construction equipped with a massive set of curling horns, fangs and backward-bending legs, giving it literally a diabolic appearance. It is powered or activated by a device called the Heart of the Muse, ✣ which was hidden separately in the former Corbettite vaults in Library territory, before being covertly retrieved by Aldin and Larana Chroma, It is stated by Library official Melissa Solera that the Library's head the Lord High Conservator will decide whether the Muse will be unleashed, Melissa not knowing that the LHC is by that point (almost certainly) dead.
See Also: Lucrezia Mongfish#Crystal