Related Clues:

• Most peculiar
• Least seen
• Superlatively scarce
• Adjective in a “Ripley’s” entry
• Most elusive
• Most valuable, perhaps
• Least likely to be spotted
• Least prevalent
• Hardest to find
• Furthest out there
• Most seldom seen
• Most off-the-wall
• Least likely
• Hardest to come by
• Like a numismatist's greatest treasure