With their past success of bringing down the Dead Red Dragon, the Players underestimated and misjudged the Night Tide Dragon to a certain extent.
After all, the Dead Red Dragon was an undead creature, and was a true dragon before it died. On the other hand, the Night Tide Dragon was a pseudo dragon like the drake of the Trinia Forest, which was why the Players weren't that worried about it and simply considered it a Boss that was a little more powerful than the average Boss.
That was exactly why the Players were taking casualties beyond what they expected.
