No feeling of dread, no slow build up of suspense, will feel worth it unless there’s some sort of payoff at the end! You need to see the nightmare unfold.
For the last exercise we leave the shadows and show the monster. They need a dramatic entrance, a description of their most horrific features and the protagonist’s reaction to the whole scene. The last part of the snippet is also important. Just because the monster is revealed, doesn’t mean that dread and suspense leave—make sure there are barriers to escaping the nightmare.
Finally, you need action! Lots of action! Even the monster is defined by their actions.
Here we go.