If you meant the 50th episode of the second series, the tone is much darker as the Barian Invasion reaches its peak.
This episode marks the beginning of the final series of duels where Yuma's friends (like Anna, Nistro, and Nelson) sacrifice themselves to buy time against the overwhelming power of the Barians. Yu-Gi-Oh! Zexal Second Episode 50
Confidence and the calm before the storm as the world's greatest duelists gather in one place. If you meant the 50th episode of the
The Barian Emperors—Girag, Alito, Mizar, Dumon, Marin, and Nash—have launched a full-scale assault on Earth. Yuma is incapacitated after a psychological clash with Nash (Shark), leaving his friends to defend the city. Yu-Gi-Oh! Zexal Second Episode 50
This episode takes place on the eve of the World Duel Carnival (WDC) finals in Heartland City.