[ ATLA ] Why did Fireloard Sozin look different in Aang's dreams?

In Book 3, Aang is having trouble sleeping due to numerous nightmares involving his upcoming battle with the Firelord, but in the first 2 nightmares, Firelord Ozai looks completely different than what he really looks like.

Aang knows what Ozai looks like, because he made that noodle art piece of him while in the Fire Nation School. There was also multiple pictures of Ozai around the Fire Nation that Aang would've seen.

Even Stranger is that in the last nightmare, Ozai looks the way he normally does.

Why does Aang imagine a different looking Firelord? Is there any reason behind this?