Shaedra

The Protean Guild is one of the ancillary guilds.  They are a guild of shape shifters.  When three representatives from the ancillary guilds meet with Genevieve Villard, it is revealed that Shaedra is actually another shapechanger and not the leader of the Protean Guild.  The imposter tries to kill Genevieve with an enchanted dagger given to her by Magus.  Genevieve manages to stun the assassin, causing it to self-destruct rather than give away its secrets. 
 
It should be noted that Shaedra, as a shapeshifter, constantly changed appearances so it is unknown what her true form looked like.