Unnamed Warlock

An "Unidentified Warlock" is an assassin first seen in "Valar Dohaeris".

Season 3
The unidentified warlock takes the form of a young girl and entices Daenerys to play while in Astapor. The ball she rolls to Dany actually contains a Manticore. Before the Manticore can strike, Ser Barristan Selmy stabs and kills the creature. The assassin runs and jumps off the dock - only to then magically appear in the distance. The warlock escapes uninjured.