Seen in: Godzilla series
Strengths: Massive size, nearly invincible, capable of rapid regeneration, and possessing a deadly atomic breath ray.
Weaknesses: Impaired maneuverability given its size, cadmium missiles, high doses of electricity (sometimes), the Oxygen Destroyer (possibly).
If the name of 'Godzilla: King of the Monsters' wasn't enough of a hint, the only thing that ever really posed a threat to Godzilla was another monumental monster. The only way a single person could pose a threat to the atomically-mutated creature is through scientific breakthrough - not Riddick's strong suit. Since Godzilla has remained undefeated for more than 50 years, there's no way Riddick could manage the task. Still, if Vin Diesel is looking to end the series on a high note, a Godzilla fight would do the trick.