Eel's End (used in games with 5-6 players) cannot be influenced directly; you must use the Guildmaster, Monarch (emulating the Guildmaster), Castdew Lofties, Red Mantis, or Magistrate to place a cube there.
Additionally, Eel's End cannot be controlled - players instead gain 10 support (points) at the end of the game for each of their influence cubes present, regardless of who has the most.