@JeremyECrawford for death saving throws, do lucky, portent and halfling luck work to replace a natural one? Or are they treated as mods?

— Sabrina Henderson (@Claire_Tigress) October 16, 2016

Lucky and the like can replace a roll of 1 or 20 for a death saving throw or an attack roll. It's replacing, not adding or subtracting. #DnD https://t.co/IDqckavFGx

— Jeremy Crawford (@JeremyECrawford) October 17, 2016