@JeremyECrawford How does the final perk of Mage Slayer interact with spells that have repeated saves, like Power Word Stun?

If they cast the spell while within 5ft of me, but then they walk away before I make saves, do I still have advantage?

— fek (@fekfekfekfek) November 27, 2017

Mage Slayer gives you advantage on saves against spells cast by someone within 5 feet of you. The spellcaster then wandering away doesn't turn that benefit off after the spell has been cast. #DnD https://t.co/5WI4RpohwR

— Jeremy Crawford (@JeremyECrawford) November 28, 2017