Possible Clues:

• Horned creature
• This, for one, is said to go on ahead, but not like 3 down
• One brief problem afoot for wonder horse
• One might horn in from you with your crop north of the Border
• Mythical beast like horned horse
• Mythical white animal with long horn
• Fabulous beast like horned horse
• Fabulous supporter of royalty
• It's just a myth that you get to Ulster sore on foot
• Lion's traditional adversary