If you're talking about a spell in which the person receiving the spell is getting harmed in any way... then most likely because the person putting a spell has history (knew the person in the past) and the other person probably did something the ''witch'' didn't like. Or because they're jealous. who knows.
The method which is not good for catching the audience's attention is the following one:
B. making an announcement ("In this essay, I will explain. . .")
It sounds too predictable and has no appealing elements to it. It is just formal, dull and run-of-the-mill.
All other alternatives show instigating ways to start an essay, that is, strategies that will make the audience thrilled, intrigued and/or amazed.