This is from the trailer promoting both part 1 and part 2 of the two part film. We can see near the beginning of the trailer, where i screencapped an over-the-shoulder shot (0:54), there is confrontation between both the protagonist and the antagonist. We see the antagonist (Lord Voldemort) about to cast a murdering spell at the protagonist (Harry Potter), but then the trailer cuts before we see what happens. This creates a great enigma in the trailer, and encourages the audience to pay and view the full film.
We can also see that the battle scene is set in what appears to be a dark, mystical forest. This creates tension within the audience as there is no one to rescue or save Harry, if he were to be harmed.