If you hit a cursed enemy with an attack, you deal extra damage. You decide whether to apply the extra damage after making the damage roll. You can deal this extra damage once per round, so if you have dealt Warlock’s Curse damage since the start of your turn, you cannot deal it again until the start of your next turn
PHB Update said:Warlock’s Curse [Revision/Addition]
Player’s Handbook, page 131
Replace the third sentence of the first paragraph with the following: “If you hit a cursed enemy with an attack, you deal extra damage.”
Add the following clause to the end of the last sentence of the first paragraph: “so if you have dealt Warlock’s Curse damage since the start of your turn, you cannot deal it again until the start of your next turn.”
A warlock has two targets cursed and then is able to damage them both with an AoE spell. Do both the targets take Curse damage or do only one of them take Curse damage?
Slightly related, if you were to use an AP to cast hellish rebuke twice on the same target, would they then take twice the damage when you got hurt (presumably yes, although it might not stack).

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.