I always have FAST agains Astos too. I always thought he was easy, except that he usually manages to kill 1 character, but after that he's very unlikely to kill any more. Depending on the party Chaos or Lich in the ToF is hard. For solo parties Kraken in the ToF is hard. In the PSX / WSC versions Chaos is way harder than the NES version. For 4 WMs the Wizards in the Marsh Cave were really hard for me. So I don't know.