Just started a new campaign that has two warlocks (genie and hexblade) as well as a Twilight cleric. The warlocks had planned to twin spam darkness/devil's sight, something our party has never done in all of our many 5th edition games. However, the twilight cleric's 2nd level channel divinity power Twilight Sanctuary states that it creates a "sphere centered on you, has a 30-foot radius, and is filled with dim light." It doesn't say how this sphere of dim light interacts with magical light or darkness. The DM said that he would "have to think about" which effect would be dominant. I hope there is an official ruling sometime soon, but until then what do you all think? Personally I would say that since you get TS at 2nd level, a level when the highest level spell anyone gets is first, it probably wouldn't overcome a 2nd level Darkness spell. But then I'm biased.