Magical curses are rarely cast, as if cast on someone for fun or purely maliciously and the person cursed has not done something seriously wrong, it tends to ricochet back on the curser. Therefore the few who do get cursed are shunned by most people as genuinely guilty,and few will help them.
The words of a wedding vow contain a strong love spell which enchants both the people who says it, so they will allways be deeply in love with each other.
Little halflings are told that if they don't behave, a demon called Santa Claus from a hell of ice will kidnap them and force them to toil making toys.
A Druid Circle that's witnessed the polution and destruction of Mankind plans to wipe out every technological race, turning the world into a Nature Nightmare.