Related Clues:

• Unlikely winner
• Unlikely victor
• Long shot
• Black Beauty, e.g.?
• Successful competitor of whom little was known, like colourless equine
• Little-known competitor like shadowy equine
• You don't know the form this nightmare may take
• You can't tell what form this nightmare will take
• It's not light, of course
• One does not know the form of such a nightmare
• It's a nightmare not knowing its form
• One does not know the form that 14 down may take
• Quite amount of mystery how it could be in 8 down
• You know little of such a nightmare
• A mysterious amount of black beauty