@JeremyECrawford Curse of Strahd: Champion Fighter accepts a dark gift, it lets him cast Contagion (it requires a melee spell attack). The Champion doesn't have any Spellcasting Ability (Charms, on DMG, don't cover this).
Which modifier must use a Champion to hit with Contagion?
— Draconis (@DerynDraconis) June 7, 2018
Sometimes a non-spellcaster gains the ability to cast a spell. If you're in that situation and a rule doesn't tell you how to calculate your spell's save DC, use the default calculation in the spellcasting rules (PH, 205), and your spellcasting ability modifier is 0. #DnD https://t.co/F4WYUluw7h
— Jeremy Crawford (@JeremyECrawford) June 11, 2018