Boon of Legendary Superiority (5e Epic Boon)
From D&D Wiki
Boon of Legendary Superiority
When you cause a creature to make a saving throw, and that creature uses legendary resistance to choose to succeed on the save, you can choose to have it make the saving throw as normal. You can use this boon 3 times. When you finish a long rest, you regain your uses of this boon.