The point of view of E.T.A. Hoffman's "The Sandman" is a combination of first person narration and third person narration.
The short story begins in the first person narrative voice. The reason for this is because the story opens with a letter written by Nathaniel. It's his letter, so he uses "I" to refer to himself.
The second section of "The Sandman" continues the first person narration, but it is being narrated by a different person. This time Clara is writing a letter to Nathaniel. Again, it's her letter, so she uses the first person "I."
The third letter is again written by Nathaniel, so the original first person narration continues.
Then a twist occurs. The story stops narrating through the letter format. Instead another narrator now enters, and he explains (in the first person) to readers that he prefaced his own narration with the three letters. Immediately following, the narrator continues to tell readers about Nathaniel, but the narrator does so from the third person perspective. The narrator occasionally switches back to first person in order to "talk" directly to readers, but for the most part he stays in the third person.