Spoiler (click to reveal)
Let's say one of my characters curses a monster. I put the curse card into the monster damage deck per the printed rules. In addition, I put a curse counter (accidentally, but thoughtfully, included in the game) on the afflicted monster and treat it like any other negative condition (stun, immobilize, etc.). The counter remains on the monster until the end of the monster's next turn. It makes Curse a little more powerful because some characters do additional damage based on the number of negative conditions on a monster, but I like being able to see the effect of having cursed a specific monster rather than the more abstract impact to the monster damage deck.