Full Counter (Magic) (5e Epic Boon)
From D&D Wiki
You have learned a demonic art, capable of reflecting powerful blows.
When you are effected by an attack or damaging effect from a spell or cantrip, you may instead reflect that damage back at the attacker as a reaction. the target must make a deterity saving throw, in addition to any other saving throw, to avoid this affect. otherwise, they are effected by the spell as if you had casted it with no components.