I'm designing a challenge that combines multiple difficult regex scenarios: 
1. Near-duplicate patterns where only specific variants should match
2. Various formats requiring precise pattern boundaries
3. Items with special regex metacharacters that need careful escaping
4. Formats that appear similar but have subtle distinguishing characteristics
5. Items that would tempt overly greedy matching or catastrophic backtracking
6. Patterns that would require negative lookahead/lookbehind or complex ... (truncated)