Lyssa's Muse is the avatar of the goddess Lyssa. It can be summoned by kneeling at any statue of Lyssa when the world has the Favor of the Gods at the time. In explorable areas, each player may - in exchange for some gold - receive a blessing of Lyssa from the Avatar.
"The glory of Lyssa is reflected in many realms. Do you dedicate this offering to one in particular?"
See Statue of Lyssa for a list of locations.