Ranger - "Higher Vampire" [5th Campaign, 5th Mission]

Mongol, when a complete set is collected, a message appears indicating that the artifact collection task has been completed. If there was no message, it means the set is incomplete.

You don't need to go to the prophet for the phoenixes because it's enough to kill all the black "freshly rotten" ones.

Indeed, that's true. However, if you don't get the phoenixes, you should stay away from Nicholas. Otherwise, there's a chance he might disappear forever. I obtained the phoenixes, left them in the nearest town, and went to fight the dragons.