Level 60 was already the highest level that a wild BOSS could reach. BOSSES that were even stronger than this level could only be encountered during quests or could only appear as a result of plot-related interactions. It was rumored that this sort of BOSSES were far cleverer, stronger, and more likely to have better loot. However, their whereabouts were like legends that would require players to meet certain criteria just to meet them, so it was far more infrequent to bump into them than wild BOSSES.
Wild BOSSES in Parallel World had been specifically programed to be mobile. This was done to prevent situations like players forming a team daily to do BOSS grinding in a set spot from cropping up. This also meant that BOSSES from all the various levels were unlike the usual monsters that would remain in their respective grinding maps and could, instead, be found roaming about.