Ainz - World Item

The elite dragons were the most powerful opponents in Yggdrasil, too, so it was dangerous to operate separately from the guardians without knowing their strength. But Ainz had a World Item. It had a few different functions, but one of them worked particularly well against dragons. That meant that even in the worst case, he would at least be able to escape. If, however, he brought the guardians, and the dragons turned out to be more powerful than expected, he would have to buy time for them to get away.

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Volume 11, Chapter 5.2