Possible Clues:

• Many-headed monster of Greek mythology
• Mythical nine-headed monster
• Hardy variety of monster
• Persistent trouble, tough, all after first round
• Sea Serpent constellation
• Mythical serpent
• Victim of Hercules' second labor
• Initially high and dry, failing to stop evil
• Opponent of Hercules, said to be continually getting ahead
• Detailing creation of Stevenson: might one paint 6 down?