I'm creating an extremely difficult challenge using multiple pattern types that must be matched with a single regex. This includes:

1. Valid IPv6 addresses in different formats (with shortened sections and full format)
2. Valid ISBN-13 codes with different separators (hyphens, spaces, none)
3. Credit card numbers with varying formats (spaces, dashes, or no separators)
4. Base64 encoded strings with padding
5. Negative lookahead/lookbehind challenges with "almost matching" patterns
6. URLs with ... (truncated)